Absorbent polymer compositions having high sorption capacities under an applied pressure

ABSTRACT

Disclosed in the present application are absorbent polymer compositions useful in the absorption of body fluids such as urine, menses and the like. In particular, the invention relates to mixed-bed ion-exchange absorbent polymer compositions having excellent absorbency performance properties in terms of absorbent capacity under a confining pressure of 0.7 psi and/or 1.4 psi. Certain mixed-bed ion-exchange absorbent polymer compositions of the present invention have excellent absorbency properties not only for a synthetic urine with a composition and ionic strength that is typical of young infants but also for a high ionic strength synthetic urine that has a composition and ionic strength that is typical of the urine of older infants and toddlers. The invention also relates to absorbent members comprising the mixed-bed ion-exchange absorbent polymer compositions, and absorbent articles comprising the absorbent members.

This is a continuation-in-part of U.S. patent application Ser. No.09/003,565 filed on Jan. 7, 1998, filed in the names of Hird, et al.,pending; which is a continuation-in-part of U.S. Provisional ApplicationSer. No. 60/038,228 filed on Feb. 19, 1997 in the name of Goldman et al.

TECHNICAL FIELD

This application relates to absorbent polymer compositions which havehigh sorption capacities under an applied load. The application furtherrelates to absorbent members comprising the absorbent polymer and toabsorbent articles comprising these absorbent members. These absorbentpolymer compositions, members, and articles are particularly useful forabsorbing body fluids such as urine and menses.

BACKGROUND OF THE INVENTION

The development of highly absorbent articles for use as disposablediapers, adult incontinence pads and briefs, and catamenial productssuch as sanitary napkins, is the subject of substantial commercialinterest. A highly desired characteristic for such products is thinness.For example, thinner diapers are less bulky to wear, fit better underclothing, and are less noticeable. They are also more compact in thepackage, making the diapers easier for the consumer to carry and store.Compactness in packaging also results in reduced distribution costs forthe manufacturer and distributor, including less shelf space required inthe store per diaper unit.

The ability to provide thinner absorbent articles such as diapers hasbeen contingent on the ability to develop relatively thin absorbentcores or members that can acquire and store large quantities ofdischarged body fluids, in particular urine. In this regard, the use ofcertain absorbent polymers often referred to as “hydrogels”,“superabsorbents”, “xerogels” or “hydrocolloids” has been particularlyimportant. See for example, U.S. Pat. No. 3,699,103 (Harper et al.),issued Jun. 13, 1972, and U.S. Pat. No. 3,770,731 (Harmon), issued Jun.20, 1972, that disclose the use of such materials (hereinafter referredto as “absorbent polymers”) in absorbent articles. Indeed, thedevelopment of thinner diapers has been the direct consequence ofthinner absorbent cores that take advantage of the ability of theseabsorbent polymers to absorb large quantities of discharged body fluids,typically when used in combination with a fibrous matrix. See forexample, U.S. Pat. No. 4,673,402 (Weisman et al.), issued Jun. 16, 1987and U.S. Pat. No. 4,935,022 (Lash et al.), issued Jun. 19, 1990, thatdisclose dual-layer core structures comprising a fibrous matrix andabsorbent polymers useful in fashioning thin, compact, nonbulky diapers.

These absorbent polymers are often made by initially polymerizingunsaturated carboxylic acids or derivatives thereof, such as acrylicacid, alkali metal (e.g., sodium and/or potassium) or ammonium salts ofacrylic acid, alkyl acrylates, and the like in the presence ofrelatively small amounts of di- or poly-functional monomers such asN,N′-methylenebisacrylamide, trimethylolpropane triacrylate, ethyleneglycol di(meth)acrylate, or triallylamine. The di- or poly-functionalmonomer materials serve to lightly cross-link the polymer chains therebyrendering them water-insoluble, yet water-swellable. These lightlycrosslinked absorbent polymers contain a multiplicity of carboxyl groupsattached to the polymer backbone. These carboxyl groups generate anosmotic driving force for the absorption of body fluids by thecrosslinked polymer network. Absorbent polymers can also be made bypolymerizing unsaturated amines or derivatives thereof in the presenceof relatively small amounts of di- or poly-functional monomers, in ananalogous fashion.

The degree of cross-linking of these absorbent polymers is an importantfactor in establishing their absorbent capacity and gel strength.Absorbent polymers useful as absorbents in absorbent members andarticles such as disposable diapers need to have adequate sorptioncapacity, as well as adequately high gel strength. Sorption capacityneeds to be sufficiently high to enable the absorbent polymer to absorbsignificant amounts of the aqueous body fluids encountered during use ofthe absorbent article. Gel strength relates to the tendency of theswollen polymer particles to deform under an applied stress, and needsto be such that the particles do not deform and fill the capillary voidspaces in the absorbent member or article to an unacceptable degree,thereby inhibiting the rate of fluid uptake or the fluid distribution bythe member/article. In general, the permeability of a zone or layercomprising swollen absorbent can be increased by increasing thecrosslink density of the polymer gel, thereby increasing the gelstrength. However, this typically also reduces the absorbent capacity ofthe gel undesirably. See, for example, U.S. Pat. No. 4,654,039 (Brandtet al.), issued Mar. 31, 1987 (reissued Apr. 19, 1988 as Reissue U.S.Pat. No. 32,649) and U.S. Pat. No. 4,834,735 (Alemany et al.), issuedMay 30, 1989.

Many absorbent polymers can exhibit gel blocking under certainconditions. “Gel blocking” occurs when particles of the absorbentpolymer deform so as to fill the capillary void spaces in the absorbentmember or article to an unacceptable degree, thereby inhibiting the rateof fluid uptake or the distribution of fluid by the member/article. Oncegel-blocking occurs, further fluid uptake or distribution takes placevia a very slow diffusion process. In practical terms, this means thatgel-blocking can substantially impede the distribution of fluids torelatively dry zones or regions in the absorbent member or article.Leakage from the absorbent article can take place well before theparticles of absorbent polymer in the absorbent article are fullysaturated or before the fluid can diffuse or wick past the “blocking”particles into the rest of the absorbent article. See U.S. Pat. No.4,834,735 (Alemany et al), issued May 30, 1989.

This gel blocking phenomenon has typically necessitated the use of afibrous matrix in which are dispersed the particles of absorbentpolymer. This fibrous matrix keeps the particles of absorbent polymerseparated from one another and provides a capillary structure thatallows fluid to reach the absorbent polymer located in regions remotefrom the initial fluid discharge point. See U.S. Pat. No. 4,834,735(Alemany et al), issued May 30, 1989. However, dispersing the absorbentpolymer in a fibrous matrix at relatively low concentrations in order tominimize or avoid gel blocking can significantly increase the bulkinessof the absorbent article or lower the overall fluid storage capacity ofthinner absorbent structures. Using low concentrations of absorbentpolymers limits somewhat the real advantage of these materials, i.e.their ability to absorb and retain large quantities of body fluids pergiven volume.

Absorbent polymers are typically lightly crosslinked polyelectrolytesthat swell in aqueous solutions of simple electrolyte, primarily as aresult of an osmotic driving force. The osmotic driving force forabsorbent polymer swelling results primarily from polyelectrolytecounterions that are dissociated from the polyelectrolyte but are keptinside the swollen polymer due to electroneutrality considerations.Absorbent polymers that contain weak-acid or weak-base groups (e.g.,carboxylic acid or amine functional groups) in their un-neutralizedforms are only slightly dissociated in urine solutions. These weak-acidor weak-base absorbent polymers must be at least partially neutralizedwith base or acid, respectively, in order to generate substantialconcentrations of dissociated counterions. Without some neutralization,these weak-acid or weak-base absorbent polymers do not swell to theirmaximum potential absorbent capacity or gel volume. In contrast, theabsorbent capacity of absorbent polymers comprising relativelystrong-acid or strong-base functional groups (e.g. sulfonic acid orquaternary ammonium hydroxide groups) are much less sensitive to thedegree of neutralization. However, the use of these strong-acid orstrong-base absorbent polymers in their un-neutralized forms has thepotential to shift the pH of the fluid in contact with the polymer tounacceptably low or high values. They also tend to have relatively fewfunctional groups per unit weight of polymer due to the high molecularweight of the repeat unit. This tends to reduce the osmotic drivingforce for fluid absorption in these materials.

Even after neutralization, the osmotic driving force for swelling andthus the absorbent capacity or gel volume of polyelectrolyte absorbentpolymers is greatly depressed by dissolved simple electrolytes normallypresent in body fluids such as urine. Reducing the concentration ofdissolved electrolyte in urine (e.g., by dilution with distilled water)can greatly increase the absorbent capacity of a polyelectrolyteabsorbent polymer.

The concentration of dissolved electrolyte in an aqueous solution can belowered substantially by appropriate mixed-bed ion-exchange techniques.(Ion-exchange columns are often used commercially to deionize water.)Electrolyte concentration is reduced by the combined effect of exchangeof dissolved cations (e.g., Na⁺) for H⁺ ions and effective exchange ofdissolved anions (e.g., Cl⁻) for OH⁻ ions. The H⁺ and OH⁻ ionseffectively combine in solution to yield H₂₀O. The degree to which amixed-bed ion-exchange system can potentially reduce electrolyteconcentration depends on the ion-exchange capacity of the system, theconcentration of dissolved simple electrolyte in the aqueous solution,and the ratio of aqueous electrolyte solution to ion-exchange polymer.

Ion-exchange resins have been used to increase the absorbent capacity ofarticles containing absorbent polymers. See, for example, U.S. Pat. No.4,818,598 issued Apr. 4, 1989 to Wong, WO 96/15163 published May 23,1996 by Palumbo et al., WO 96/151180 published May 23, 1996 by Palumboet al., Japanese Kokai Publication 57045057A published Mar. 13, 1982,and Japanese Kokai Publication 57035938A published Feb. 26, 1982.However, the need to incorporate relatively large quantities ofion-exchange resins with relatively low ion-exchange capacity and littleor no absorbent capacity generally increases the bulk and the cost ofthe absorbent article to an unacceptable degree.

A mixture of an absorbent polymer containing unneutralized acid groupsand an absorbent polymer containing unneutralized base groups has thepotential to function as a mixed-bed ion-exchange system and effectivelyreduce the concentration of dissolved simple electrolyte in solution.Furthermore, if the absorbent polymer in a mixed-bed ion-exchange systemcontains weak acid groups which start off in their un-neutralized form,then the resulting exchange of H⁺ by e.g., Na⁺ results in the conversionof the absorbent polymer from its un-neutralized to neutralized form.Thus, the osmotic driving force for swelling (and hence the absorptioncapacity) of a weak acid absorbent polymer increases as a result ofion-exchange in such a mixed-bed ion-exchange absorbent system.Similarly, if the absorbent polymer in a mixed-bed ion-exchange systemcontains weak base groups that start off in their un-neutralized form,then the resulting effective exchange of OH⁻ by, e.g., Cl⁻ (or theaddition of HCl to a free amine group) results in the conversion of theabsorbent polymer from its un-neutralization to neutralized form. Thus,the osmotic driving force for swelling of a weak base absorbent polymeralso increases as a result of ion-exchange in a mixed-bed absorbentsystem. Effective neutralization of all of the weak acid or weak basegroups in an absorbent polymer (i.e. complete neutralization) does notnecessarily occur at neutral pH. Effective neutralization of somefraction of the weak acid and/or weak base groups (i.e. partialneutralization) is likely to occur in mixed-bed ion-exchange systemscomprising these polymers. The use of mixed-bed ion-exchange absorbentpolymers to increase absorption capacity has been described in PCTApplications WO 96/17681 (Palumbo; published Jun. 13, 1996), WO 96/15162(Fornasari et al.; published May 23, 1996), and U.S. Pat. No. 5,274,018(Tanaka; issued Dec. 28, 1993).

In an absorbent member (e.g., a blend of absorbent polymers andcellulose fiber), only a portion of the total fluid contained in themember is absorbed by the absorbent polymer. The balance of the fluid istypically absorbed by other components (e.g., in pores formed by thefiber structure). However, even though this fluid is not absorbed by theabsorbent polymer, the dissolved electrolyte in this fluid can diffuseinto the absorbent polymer. Reducing the quantity of fiber (or othernon-absorbent-polymer components capable of absorbing fluid) minimizesthe quantity of extra solution and thus the quantity of extra salt thatmust be exchanged in order to achieve a given reduction in electrolyteconcentration. Thus, mixed-bed ion-exchange absorbent polymer systemsprovide the most benefit, in terms of maximizing the absorbent capacity,in absorbent members containing relatively high concentrations ofabsorbent polymer.

Although mixed-bed ion-exchange absorbent-polymers in an absorbentmember can increase the osmotic driving force for swelling, this hasheretofore not resulted in the anticipated improvement in absorbencyperformance in terms of absorbent capacity under confining pressures of0.7 psi or greater, which is believed to be typical of the usagepressures encountered by an absorbent member during wear of an absorbentarticle. Under such confining pressures, previously disclosed mixed-bedion-exchange absorbent polymers tend to deform so as to fill thecapillary void spaces between the particles, thereby inhibiting the rateof fluid uptake. As a result, the absorption capacities of previouslydisclosed mixed-bed ion-exchange absorbent polymers are notsignificantly greater than the absorption capacities of a conventionalabsorbent polymer under confining pressures of 0.7 psi or greater.

Accordingly, it would be desirable to provide a composition comprisingabsorbent polymers capable of absorbing a large quantity of a syntheticurine solution under confining pressures of 0.7 psi or greater. It isfurther desired that the relatively high capacity be attained within atime period that is typically less than the duration of use (e.g.,overnight) of articles comprising the present absorbent compositions. Inthis regard, it is desirable that the absorbent polymers attain a highcapacity within a period of, e.g. 2, 4, 8, or 16 hours. It would furtherbe desirable to provide an absorbent polymer system having high porosityand/or permeability, as well as good integrity of the gel bed. Stillfurther, it would be desirable if such absorbent polymers also have highcapacity when exposed to a synthetic urine having the high ionicstrength more typical of older infants and toddlers.

SUMMARY OF THE INVENTION

The present invention relates to absorbent materials useful in thecontainment of body fluids such as urine. In particular, the inventionrelates to absorbent materials having excellent absorbency performanceproperties in terms of absorbent capacity under a confining pressure of0.7 psi and/or 1.4 psi.

In one aspect, the present invention relates to a mixed-bed ion-exchangeabsorbent polymer composition having a Performance Under Pressurecapacity in synthetic urine solution (hereafter “PUP” or “PUP capacity”)of at least about 30 g/g under a confining pressure of 0.7 psi (4.8 kPa)after 2 hours. (The method for measuring PUP capacity at a givenpressure for a given period of time is described in the Test Methodssection below). In another aspect, the present invention relates to amixed-bed ion-exchange absorbent polymer composition having a CapacityUnder Pressure in a high ionic strength synthetic urine solution(hereafter “CUP”) of at least about 25 g/g under a confining pressure of0.7 psi (4.8 kPa) after 2 hours. (The method for measuring CUP at agiven pressure for a given period of time is described in the TestMethods section below). In still another aspect, the invention relatesto a mixed-bed ion-exchange absorbent polymer composition having a PUPcapacity of at least about 36 g/g under a confining pressure of 0.7 psi(4.8 kPa) after 4 hours. In still another aspect, the present inventionrelates to a mixed-bed ion-exchange absorbent polymer composition havinga PUP capacity of at least about 40 g/g under a confining pressure of0.7 psi after 8 hours. In yet another aspect, the present inventionrelates to a mixed-bed ion-exchange absorbent polymer composition havinga PUP capacity of at least about 42 g/g under a confining pressure of0.7 psi after 16 hours. As used herein, the term “after” meansimmediately after.

In another aspect, the present invention relates to a mixed-bedion-exchange absorbent polymer composition having a PUP capacity of atleast about 24 g/g under a confining pressure of 1.4 psi (9.6 kPa) after2 hours. In still another aspect, the present invention relates to amixed-bed ion-exchange absorbent polymer composition having a PUPcapacity of at least about 27 g/g under a confining pressure of 1.4 psiafter 4 hours. In yet another aspect, the present invention relates to amixed-bed ion-exchange absorbent polymer composition having a PUPcapacity of at least about 30 g/g under a confining pressure of 1.4 psiafter 8 hours. In still another aspect, the present invention relates toa mixed-bed ion-exchange absorbent polymer composition having a PUPcapacity of at least about 33 g/g under a confining pressure of 1.4 psiafter 16 hours.

In a preferred embodiment, the invention relates to a compositioncomprising cation-exchange absorbent polymers that contain weak-acidgroups in their un-neutralized form, and anion-exchange absorbentpolymers that contain weak-base groups in their un-neutralized form,wherein the mixture exhibits high absorbence of a synthetic urinesolution under PUP- and/or CUP absorption conditions within a timeperiod that is less than the duration of use (e.g., overnight) ofarticles comprising the present absorbent compositions. In this regard,the mixed-bed ion-exchange absorbent polymers will exhibit this improvedabsorbency when PUP and/or CUP capacity is measured for a period of,e.g. 2, 4, 8, and/or 16 hours. The invention also relates to absorbentmembers comprising the above-described absorbent polymer compositions,and to absorbent articles comprising such absorbent members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a schematic view of an apparatus for measuring thePerformance under Pressure (PUP) capacity of absorbent polymers.

FIG. 2 represents an enlarged sectional view of the piston/cylinderassembly shown in FIG. 1.

FIG. 3 graphically depicts PUP capacity data for absorbent polymercompositions of the present invention and the prior art, where PUPcapacity is measured under a confining pressure of 0.7 psi.

FIG. 4 graphically depicts PUP capacity data for absorbent polymercompositions of the present invention and the prior art, where PUPcapacity is measured under a confining pressure of 1.4 psi.

FIG. 5 graphically depicts CUP data for absorbent polymer compositionsof the present invention and the prior art, where CUP is measured undera confining pressure of 0.7 psi.

FIG. 6 graphically depicts CUP data for absorbent polymer compositionsof the present invention and the prior art, where CUP is measured undera confining pressure of 1.4 psi.

FIG. 7 represents a schematic view of an apparatus for preparing anabsorbent polymer composition sample for measurement of thecomposition's Ball Burst Strength (BBS).

FIG. 8 represents a schematic view of an apparatus for measuring theBall Burst Strength (BBS) of an absorbent polymer composition.

DETAILED DESCRIPTION OF THE INVENTION

A. Definitions

As used herein, the term “body fluids” includes urine, blood, menses andvaginal discharges.

As used herein, the term “synthetic urine solution” refers to an aqueoussolution prepared by dissolving 2.0 g KCl, 2.0 g Na₂SO₄, 0.85 gNH₄H₂PO₄, 0.15 g (NH₄)₂HPO₄, 0.25 g CaCl₂.2H₂O, and 0.50 g MgCl₂.6H₂O indistilled water to yield one liter of solution.

As used herein, the term “high ionic strength synthetic urine solution”refers to an aqueous solution prepared by dissolving 4.0 g KCl, 2.0 gNa₂SO₄, 1.2 g NH₄H₂PO₄, 1.6 g (NH₄)₂HPO₄, 0.20 g CaCl₂.2H₂O, 0.55 gMgCl₂.6H₂O, and 7.0 g NaCl in distilled water to yield one liter ofsolution.

As used herein, the term “ion-exchange capacity” refers to thetheoretical or calculated ion-exchange capacity of the polymer orpolymers in milliequivalents per gram assuming that each unneutralizedacid or base group becomes neutralized in the ion-exchange process.

As used herein, the term “absorbent polymer” refers to a polymer whichis capable of absorbing within the polymer at least 10 times its weightin deionized water, allowing for adjustment of the pH of the system.

As used herein, the term “absorbent core” refers to the component of theabsorbent article that is primarily responsible for fluid handlingproperties of the article, including acquiring, transporting,distributing and storing body fluids. As such, the absorbent coretypically does not include the topsheet or backsheet of the absorbentarticle.

As used herein, the term “absorbent member” refers to the components ofthe absorbent core that typically provide one or more fluid handlingproperties, e.g., fluid acquisition, fluid distribution, fluidtransportation, fluid storage, etc. The absorbent member can comprisethe entire absorbent core or only a portion of the absorbent core, i.e.,the absorbent core can comprise one or more absorbent members. Theimproved mixed-bed ion-exchange absorbent polymer compositions describedherein are particularly useful in absorbent members whose primaryfunction is the storage of aqueous body fluids. However, thesecompositions may also be present in other absorbent members.

As used herein, the terms “region(s)” or “zone(s)” refer to portions orsections, in a macroscopic sense, of an absorbent member.

As use herein, the term “layer” refers to a portion of an absorbentarticle whose primary dimensions are along its length and width. Itshould be understood that the term layer is not necessarily limited tosingle layers or sheets of material. Thus the layer can be comprised oflaminates or combinations of several sheets or webs of the requisitetype of materials. Accordingly, the term “layer” includes the terms“layers” and “layered.”

As used herein, the term “comprising” means that various components,members, steps and the like can be conjointly employed according to thepresent invention. Accordingly, the term “comprising” encompasses themore restrictive terms “consisting essentially of” and “consisting of,”these latter, more restrictive terms having their standard meaning asunderstood in the art.

All percentages, ratios and proportions used herein are by weight unlessotherwise specified.

B. Mixed-Bed Ion-Exchange Absorbent Polymer Compositions

The present invention relates, in part, to mixed-bed ion-exchangeabsorbent polymer compositions that exhibit very high absorbency ofsynthetic urine solution under an applied load. These mixed-bedion-exchange absorbent polymer compositions comprise mixtures ofanion-exchange absorbent polymers and cation-exchange absorbentpolymers, as described in detail below.

1. Chemical Composition

a. Anion-Exchange Absorbent Polymers

The anion-exchange absorbent polymer(s) containing weak-base groupsinclude a variety of water-insoluble, but water-swellable polymers.These are typically lightly crosslinked polymers which contain amultiplicity of base functional groups, such as primary, secondaryand/or tertiary amines; or the corresponding phosphines. Examples ofpolymers suitable for use herein include those which are prepared frompolymerizable monomers which contain base groups, or groups which can beconverted to base groups after polymerization. Thus, such monomersinclude those which contain primary, secondary and/or tertiary amines;or the corresponding phosphines. Representative monomers include, butare not limited to, ethylenimine (aziridine), allylamine, diallylamine,4-aminobutene, alkyl oxazolines, vinylformamide, 5-aminopentene,carbodiimides, formaldazine, melamine and the like, as well as theirsecondary or tertiary amine derivatives.

Some monomers which do not contain base groups can also be included,usually in minor amounts, in preparing the anion-exchange absorbentpolymers herein. The absorbent polymers described herein can behomopolymers, copolymers (including terpolymers and higher ordercopolymers), or mixtures (blends) of different homopolymers orcopolymers. The polymers may also be random, graft, or block copolymers,and may have linear or branched architectures.

The polymers are rendered water-insoluble, but water-swellable, by arelatively low degree of crosslinking. This may be achieved by includingthe appropriate amount of a suitable crosslinking monomer during thepolymerization reaction. Examples of crosslinking monomers includeN,N′-methylenebisacrylamide, ethylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, triallylamine, diaziridinecompounds, and the like. Alternatively, the polymers can be crosslinkedafter polymerization by reaction with a suitable crosslinking agent suchas di- or poly-halogenated compounds and/or di- or poly-epoxy compounds.Examples include diiodopropane, dichloropropane, ethylene glycoldiglycidyl ether, and the like. The crosslinks may be homogeneouslydistributed throughout the gel particle, or may be preferentiallyconcentrated at or near the surface of the particle.

While the anion-exchange absorbent polymer is preferably of one type(i.e., homogeneous), mixtures of anion-exchange polymers can also beused in the present invention. For example, mixtures of crosslinkedpolyethylenimine and crosslinked polyallylamine can be used in thepresent invention.

When used as part of a mixed-bed ion-exchange composition, theanion-exchange absorbent polymer starts off from about 50% to about100%, preferably about 80% to about 100%, more preferably from about 90%to about 100%, in the un-neutralized base form.

In order to maximize the ion-exchange capacity of the mixed-bedion-exchange absorbent polymer composition, it is desirable that theabsorbent polymer have a high ion-exchange capacity per gram of drypolymer. Thus, it is preferred that the ion-exchange capacity of theanion-exchange absorbent polymer component is at least about 10 meq/g,more preferably at least about 15 meq/g, and most preferably at leastabout 20 meq/g.

b. Cation-Exchange Absorbent Polymers

Absorbent polymers useful as cation exchanger(s) typically have amultiplicity of acid functional groups such as carboxylic acid groups.Examples of cation-exchange polymers suitable for use herein includethose which are prepared from polymerizable, acid-containing monomers,or monomers containing functional groups which can be converted to acidgroups after polymerization. Thus, such monomers include olefinicallyunsaturated carboxylic acids and anhydrides and mixtures thereof. Thecation-exchange polymers can also comprise polymers that are notprepared from olefinically unsaturated monomers. Examples of suchpolymers include polysaccharide-based polymers such as carboxymethylstarch and carboxymethyl cellulose, and poly(amino acid) based polymerssuch as poly(aspartic acid). For a description of poly(amino acid)absorbent polymers, see, for example, U.S. Pat. No. 5,247,068, issuedSep. 21, 1993 to Donachy et al., which is incorporated herein byreference.

Some non-acid monomers can also be included, usually in minor amounts,in preparing the absorbent polymers herein. Such non-acid monomers caninclude, for example, monomers containing the following types offunctional groups: carboxylate or sulfonate esters, hydroxyl groups,amide-groups, nitrile groups, and aryl groups (e.g., phenyl groups, suchas those derived from styrene monomer). Other optional non-acid monomersinclude unsaturated hydrocarbons such as ethylene, propylene, 1-butene,butadiene, and isoprene. These non-acid monomers are well-knownmaterials and are described in greater detail, for example, in U.S. Pat.No. 4,076,663 (Masuda et al.), issued Feb. 28, 1978, and in U.S. Pat.No. 4,062,817 (Westerman), issued Dec. 13, 1977, both of which areincorporated by reference.

Olefinically unsaturated carboxylic acid and anhydride monomers includethe acrylic acids typified by acrylic acid itself, methacrylic acid,α-chloroacrylic acid, α-cyanoacrylic acid, β-methylacrylic acid(crotonic acid), α-phenylacrylic acid, β-acryloxypropionic acid, sorbicacid, α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamicacid, β-stearylacrylic acid, itaconic acid, citroconic acid, mesaconicacid, glutaconic acid, aconitic acid, maleic acid, fumaric acid,tricarboxyethylene, and maleic anhydride.

Preferred cation-exchange absorbent polymers contain carboxyl groups.These polymers include hydrolyzed starch-acrylonitrile graft copolymers,partially neutralized hydrolyzed starch-acrylonitrile graft copolymers,starch-acrylic acid graft copolymers, partially neutralizedstarch-acrylic acid graft copolymers, hydrolyzed vinyl acetate-acrylicester copolymers, hydrolyzed acrylonitrile or acrylamide copolymers,slightly network crosslinked polymers of any of the foregoingcopolymers, polyacrylic acid, and slightly network crosslinked polymersof polyacrylic acid. These polymers can be used either alone or in theform of a mixture of two or more different polymers. Examples of thesepolymer materials are disclosed in U.S. Pat. No. 3,661,875, U.S. Pat.No. 4,076,663, U.S. Pat. No. 4,093,776, U.S. Pat. No. 4,666,983, andU.S. Pat. No. 4,734,478.

Most preferred polymer materials for use in making the cation-exchangeabsorbent polymers are slightly network crosslinked polymers ofpolyacrylic acids and starch derivatives thereof. Network crosslinkingrenders the polymer substantially water-insoluble and, in part,determines the absorptive capacity and extractable polymer contentcharacteristics of the absorbent polymers. Processes for networkcrosslinking these polymers and typical network crosslinking agents aredescribed in greater detail in U.S. Pat. No. 4,076,663.

While the cation-exchange absorbent polymer is preferably of one type(i.e., homogeneous), mixtures of cation-exchange polymers can also beused in the present invention. For example, mixtures of starch-acrylicacid graft copolymers and slightly network crosslinked polymers ofpolyacrylic acid can be used in the present invention.

When used as part of a mixed-bed ion-exchange composition, thecation-exchange absorbent polymer starts off from about 50% to about100%, preferably about 80% to about 100%, more preferably from about 90%to about 100%, in the un-neutralized acid form.

In order to maximize the ion-exchange capacity of the mixed-bedion-exchange absorbent polymer composition, it is desirable that thecation-exchange absorbent polymer has a high ion-exchange capacity pergram of dry polymer. Thus it is preferred that the ion-exchange capacityof the cation-exchange absorbent polymer component is at least about 4meq/g, more preferably at least about 8 meq/g, even more preferably atleast about 10 meq/g, and most preferably at least about 13 meq/g.

c. Composition and Common Material Properties

The equivalents of anionic and cationic exchange capacity may be equalor different in the mixed-bed ion-exchange absorbent polymercomposition. For example, it may be desirable to have somewhat moreequivalents of anionic or cationic ion-exchange absorbent polymer, e.g.,to compensate for differences in pK, to compensate for differences inneutralization, to alter the pH of (for example to acidify) theion-exchanged urine, etc.

Mixed-bed ion-exchange absorbent polymer compositions inhigh-concentration absorbent cores cannot rely on solution flow,stirring, etc. to help transport ions and accelerate the rate of ionexchange. Thus it is desirable to have particle morphologies suitablefor promoting fast ion-exchange kinetics. Desirable morphologies include(i) mixed-bed aggregates of high-surface-area (e.g., small and/orporous) particles with a broad or narrow particle size distribution,(ii) particles of, e.g., the anion-exchange absorbent polymer thatcontain within smaller discontinuous domains of, e.g., thecation-exchange absorbent polymer, and (iii) particles that containbicontinuous domains of both anion- and cation-exchange absorbentpolymers.

Mixed-bed ion-exchange absorbent polymer compositions with theabove-described morphologies can be prepared using various mixingtechniques as are well known to the art. Exemplary blending techniquesinclude: high shear blending, ball milling, pin milling, and the like.As will also be obvious to one skilled in the art, mixing and/orblending of the components may be performed prior to, or after thedrying step in the manufacturing process. Additives or process aids suchas water, glycerol, oils, silica, or mixtures thereof may be added tothe components being blended to facilitate mixing.

The absorbent polymers can also comprise mixtures with low levels of oneor more additives, such as, e.g., powdered silica, surfactants, glues,binders, and the like. The components in this mixture can be physicallyand/or chemically associated in a form such that the absorbent polymercomponent and the non-absorbent polymer additive are not readilyphysically separable. The absorbent polymers can be essentiallynon-porous (i.e., no internal porosity) or have substantial internalporosity. In the mixed-bed absorbent polymer composition, the absorbentpolymer of one type can have a higher crosslink density than theabsorbent polymer of the other type.

For particles of absorbent polymers useful in the present invention, theparticles will generally range in size from about 1 to about 2000microns, more preferably from about 20 to about 1000 microns. The massmedian particle size will generally be from about 20 to about 1500microns, more preferably from about 50 microns to about 1000 microns,and even more preferably from about 100 to about 800 microns.

An important characteristic of absorbent polymers is the level ofextractables present in the polymer itself. See U.S. Pat. No. 4,654,039(Brandt et al.), issued Mar. 31, 1987 (reissued Apr. 19, 1988 as ReissueU.S. Pat. No. 32,649), the disclosure of each of which is incorporatedherein by reference. Many absorbent polymers contain significant levelsof extractable polymer material which can be leached out of the swollenpolymer matrix by body fluids (e.g., urine) during the time period thatsuch body fluids remain in contact with the absorbent polymer. It isbelieved such polymer material extracted by body fluid in this mannercan alter both the chemical and physical characteristics of the bodyfluid to the extent that the fluid is more slowly absorbed and morepoorly held by the absorbent polymer in the absorbent article. It isalso believed that extractable polymer is particularly deleterious inmixed-bed ion-exchange absorbent polymer systems because soluble polymerwill tend to migrate to gel particles comprised of oppositely chargedpolymer. The two polymers will self-neutralize, thereby reducing theion-exchange capacity of the system. Because extractable polymereffectively comprises a polyvalent counterion to the oppositely chargedpolymer, it can also form ionic crosslinks which inhibit the ability ofthe gel to swell.

Accordingly, for ion-exchange absorbent polymers of the presentinvention, it is preferred that the level of extractable polymer beabout 15% or less, more preferably about 10% or less, and mostpreferably about 7% or less, of the total polymer.

2. Physical Properties

a. Performance Under Pressure (PUP)

Measurement of the Demand Wettability or Gravimetric Absorbance canprovide information on the ability of a high concentration zone or layerof the absorbent polymer to absorb body fluids under usage pressures.See, for example, U.S. Pat. No. 5,562,646 (Goldman et al.) issued Oct.8, 1996 and U.S. Pat. No. 5,599,335 (Goldman et al.) issued Feb. 4, 1997where Demand Wettability or Gravimetric Absorbence is referred to asPerformance Under Pressure (PUP). In a PUP measurement, an initially-dryabsorbent polymer composition at 100% concentration is positioned in apiston/cylinder apparatus (where the bottom of the cylinder is permeableto solution, but impermeable to the absorbent polymer) under amechanical confining pressure and is allowed to absorb synthetic urinesolution under demand-absorbency conditions at zero hydrostatic suctionand high mechanical pressure. The “PUP” capacity is defined as the g/gabsorption of a synthetic urine solution having a composition and ionicstrength typical of young infants by a 0.032 g/cm² layer of theabsorbent polymer, while being confined under a specific appliedpressure for a particular time period. A high PUP capacity is acritically important property for an absorbent polymer when it is usedat high concentrations in an absorbent member.

Usage pressures exerted on the absorbent polymers include bothmechanical pressures (e.g., exerted by the weight and motions of theuser, taping forces, etc.) and capillary pressures (e.g., the capillarydesorption pressure of the acquisition component(s) in the absorbentcore that temporarily hold fluid before it is absorbed by the absorbentpolymer). It is believed that a total pressure of about 0.7 psi (4.8kPa) is reflective of the sum of these pressures on the mixed-bedabsorbent polymer composition as it absorbs body fluids under usageconditions. However, both higher and lower pressures can also beexperienced by the absorbent polymer composition under usage conditions.Thus, it is desirable that the mixed-bed ion-exchange absorbent polymersof the present invention have high PUP capacities at pressures up toabout 1.4 psi (9.6 kPa). It is preferred that the relatively high PUPcapacity values be attained within a time period that is less than theduration of use (e.g., overnight) of articles comprising the presentabsorbent compositions. In this regard, the mixed-bed ion-exchangeabsorbent polymers will exhibit this improved absorbency when PUPcapacity is measured for a period of, e.g. 2, 4, 8, and/or 16 hours.

A method for determining the PUP capacities of these absorbent polymersis described in the Test Methods section below. The method is based onthe procedure described in U.S. Pat. No. 5,562,646 (Goldman et al.)issued Oct. 8, 1996 (incorporated herein by reference), and is modifiedto run for longer periods of time under various desired confiningpressures, in order to simulate particular in-use conditions moreclosely.

(i) PUP Capacity Under a Confining Pressure of 0.7 psi

The mixed-bed ion-exchange absorbent polymer compositions of the presentinvention are described, in one aspect, in terms of their ability toabsorb synthetic urine under confining pressure of 0.7 psi. In thisregard, the invention relates to a mixed-bed ion-exchange absorbentpolymer composition having a Performance Under Pressure capacity insynthetic urine solution of at least about 30 g/g under a confiningpressure of 0.7 psi after 2 hours. Preferably, the polymer compositionwill have a PUP capacity in synthetic urine solution of at least about32 g/g, more preferably at least about 35 g/g and most preferably atleast about 38 g/g after 2 hours, under a confining pressure of 0.7 psi.Typically, the polymer composition will have a PUP capacity of fromabout 30 g/g to about 49 g/g, more typically from about 32 g/g to about47 g/g, still more typically from about 35 g/g to about 45 g/g, andstill more typically from about 38 g/g to about 43 g/g after 2 hours,under a confining pressure of 0.7 psi.

In a similar aspect, the invention relates to a mixed-bed ion-exchangeabsorbent polymer composition having a Performance Under Pressurecapacity in synthetic urine solution of at least about 36 g/g under aconfining pressure of 0.7 psi after 4 hours. Preferably, the polymercomposition will have a PUP capacity in synthetic urine solution of atleast about 38 g/g, more preferably at least about 40 g/g and mostpreferably at least about 42 g/g after 4 hours, under a confiningpressure of 0.7 psi. Typically, the polymer composition will have a PUPcapacity of from about 36 g/g to about 55 g/g, more typically from about38 g/g to about 52 g/g, still more typically from about 40 g/g to about50 g/g, and still more typically from about 42 g/g to about 48 g/g after4 hours, under a confining pressure of 0.7 psi.

In a similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a PUP capacity in synthetic urine solution of atleast about 40 g/g under a confining pressure of 0.7 psi after 8 hours.Preferably, the polymer composition will have PUP capacity of at leastabout 42 g/g, more preferably at least about 44 g/g and most preferablyat least about 46 g/g after 8 hours, under a confining pressure of 0.7psi. Typically, the polymer composition will have a PUP capacity of fromabout 40 g/g to about 59 g/g, more typically from about 42 g/g to about57 g/g, still more typically from about 44 g/g to about 55 g/g, andstill more typically from about 46 g/g to about 52 g/g after 8 hours,under a confining pressure of 0.7 psi.

In another similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a PUP capacity of at least about 42 g/g under aconfining pressure of 0.7 psi after 16 hours. Preferably, the polymercomposition will have PUP capacity of at least about 44 g/g, morepreferably at least about 46 g/g and most preferably at least about 48g/g after 16 hours, under a confining pressure of 0.7 psi. Typically,the polymer composition will have a PUP capacity of from about 42 g/g toabout 61 g/g, more typically from about 44 g/g to about 59 g/g, stillmore typically from about 46 g/g to about 57 g/g, and still moretypically from about 48 g/g to about 54 g/g after 16 hours, under aconfining pressure of 0.7 psi.

(ii) PUP Capacity Under a Confining Pressure of 1.4 psi

The mixed-bed ion-exchange absorbent polymer compositions are separatelydescribed in terms of their ability to absorb synthetic urine under aconfining pressure of 1.4 psi. Of course, it will be recognized thatcertain absorbent materials will exhibit the described absorbencyproperties at both 0.7 psi and 1.4 psi.

In this regard, the invention relates to a mixed-bed ion-exchangeabsorbent polymer composition having a PUP capacity, after 2 hours, ofat least about 24 g/g under a confining pressure of 1.4 psi. Preferably,the polymer composition will have a PUP capacity after 2 hours of atleast about 26 g/g, more preferably at least about 28 g/g and mostpreferably at least about 30 g/g, under a confining pressure of 1.4 psi.Typically, the polymer composition will have a PUP capacity after 2hours of from about 24 g/g to about 40 g/g, more typically from about 26g/g to about 38 g/g, still more typically from about 28 g/g to about 36g/g, and still more typically from about 30 g/g to about 35 g/g, under aconfining pressure of 1.4 psi.

In a similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a PUP capacity, after 4 hours, of at least about27 g/g under a confining pressure of 1.4 psi. Preferably, the polymercomposition will have a PUP capacity after 4 hours of at least about 29g/g, more preferably at least about 32 g/g and most preferably at leastabout 35 g/g, under a confining pressure of 1.4 psi. Typically, thepolymer composition will have a PUP capacity after 4 hours of from about27 g/g to about 46 g/g, more typically from about 29 g/g to about 44g/g, still more typically from about 32 g/g to about 42 g/g, and stillmore typically from about 35 g/g to about 40 g/g, under a confiningpressure of 1.4 psi.

In a similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a PUP capacity, after 8 hours, of at least about30 g/g under a confining pressure of 1.4 psi. Preferably, the polymercomposition will have a PUP capacity after 8 hours of at least about 32g/g, more preferably at least about 35 g/g and most preferably at leastabout 37 g/g, under a confining pressure of 1.4 psi. Typically, thepolymer composition will have a PUP capacity after 8 hours of from about30 g/g to about 49 g/g, more typically from about 32 g/g to about 47g/g, still more typically from about 35 g/g to about 45 g/g, and stillmore typically from about 37 g/g to about 43 g/g, under a confiningpressure of 1.4 psi.

In another similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a PUP capacity, after 16 hours, of at least about33 g/g under a confining pressure of 1.4 psi. Preferably, the polymercomposition will have a PUP capacity after 16 hours of at least about 35g/g, more preferably at least about 38 g/g and most preferably at leastabout 40 g/g, under a confining pressure of 1.4 psi. Typically, thepolymer composition will have a PUP capacity after 16 hours of fromabout 33 g/g to about 52 g/g, more typically from about 35 g/g to about50 g/g, still more typically from about 38 g/g to about 48 g/g, andstill more typically from about 40 g/g to about 45 g/g, under aconfining pressure of 1.4 psi.

b. As noted above, PUP capacity provides important information on theabsorbence of a synthetic urine by an absorbent polymer composition. Itshould be noted, however, that the synthetic urine used for PUPmeasurements is based on the composition of the urine of infants thatare relatively young. As is known, the composition of urine changes asan infant matures for such reasons as dietary changes, bodily organmaturation, additional activity, etc. It is also recognized thatabsorbent articles are typically worn by such older infants and toddlersuntil they are toilet trained. As a result, there is a need for measuresof performance of absorbent polymer compositions upon exposure to urinethat is typical of such older infants and toddlers. The CUP test that isdescribed in the TEST METHODS section below is one such measure.Essentially “CUP” is measured in the same manner as “PUP” capacityexcept a synthetic urine having a high ionic strength and a compositionthat is typical of the urine of older infants or toddlers is used as thetest fluid. As such, “CUP” is defined as the g/g absorption of asynthetic urine solution having a composition and ionic strength typicalof older infants or toddlers by a 0.032 g/cm² layer of the absorbentpolymer, while being confined under a specific applied pressure for aparticular time period. As will be recognized absorbent polymercompositions having both a high PUP capacity and a high CUP will beparticularly useful in absorbent members and absorbent articles.

(i) CUP Under a Confining Pressure of 0.7 psi

The mixed-bed ion-exchange absorbent polymer compositions of the presentinvention are further described, in one aspect, in terms of theirability to absorb high ionic strength synthetic urine under a confiningpressure of 0.7 psi. In this regard, the invention relates to amixed-bed ion-exchange absorbent polymer composition having a CapacityUnder Pressure in high ionic strength synthetic urine solution of atleast about 23 g/g under a confining pressure of 0.7 psi after 1 hour.Typically, the polymer composition will have a CUP of between about 23g/g and about 35 g/g, under a confining pressure of 0.7 psi after 1hour.

In a similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a CUP in high ionic strength synthetic urinesolution of at least about 25 g/g under a confining pressure of 0.7 psiafter 4 hours. Preferably, the polymer composition will have a CUP inhigh ionic strength synthetic urine solution of at least about 27 g/g,more preferably at least about 30 g/g after 4 hours, under a confiningpressure of 0.7 psi. Typically, the polymer composition will have a CUPof from about 25 g/g to about 35 g/g, more typically from about 27 g/gto about 33 g/g, after 4 hours, under a confining pressure of 0.7 psi.

In another similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a CUP in high ionic strength synthetic urinesolution of at least about 27 g/g under a confining pressure of 0.7 psiafter 8 hours. Preferably, the polymer composition will have CUP of atleast about 29 g/g, more preferably at least about 31 g/g after 8 hours,under a confining pressure of 0.7 psi. Typically, the polymercomposition will have a CUP of from about 27 g/g to about 37 g/g, moretypically from about 29 g/g to about 33 g/g after 8 hours, under aconfining pressure of 0.7 psi.

(ii) CUP Under a Confining Pressure of 1.4 psi

The mixed-bed ion-exchange absorbent polymer compositions are separatelydescribed in terms of their ability to absorb synthetic urine under aconfining pressure of 1.4 psi. Of course, it will be recognized thatcertain absorbent materials will exhibit the described absorbencyproperties at both 0.7 psi and 1.4 psi.

In this regard, the invention relates to a mixed-bed ion-exchangeabsorbent polymer composition having a CUP, after 2 hours, of at leastabout 20 g/g under a confining pressure of 1.4 psi. Preferably, thepolymer composition will have a CUP after 2 hours of at least about 23g/g and more preferably at least about 27 g/g, under a confiningpressure of 1.4 psi. Typically, the polymer composition will have a CUPafter 2 hours of from about 20 g/g to about 35 g/g, more typically fromabout 23 g/g to about 32 g/g, and still more typically from about 23 g/gto about 30 g/g under a confining pressure of 1.4 psi.

In a similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a CUP, after 8 hours, of at least about 22 g/gunder a confining pressure of 1.4 psi. Preferably, the polymercomposition will have a CUP after 8 hours of at least about 25 g/g andmore preferably at least about 27 g/g, under a confining pressure of 1.4psi. Typically, the polymer composition will have a CUP after 8 hours offrom about 22 g/g to about 35 g/g and more typically from about 25 g/gto about 33 g/g, under a confining pressure of 1.4 psi.

In another similar aspect, the mixed-bed ion-exchange absorbent polymercomposition will have a CUP, after 16 hours, of at least about 25 g/gunder a confining pressure of 1.4 psi. Preferably, the polymercomposition will have a CUP, after 16 hours, of at least about 27 g/g,under a confining pressure of 1.4 psi. Typically, the polymercomposition will have a CUP after 16 hours of from about 25 g/g to about35 g/g, under a confining pressure of 1.4 psi.

c. Permeability of the Zone or Layer Comprising Absorbent Polymer

An important property of zones or layers comprising absorbent polymersis their permeability to fluid. In an absorbent member or article, thisdirectly affects the ability of a material, such as the layer comprisingthe swollen absorbent polymer to transport body fluids away from theacquisition region at an acceptable rate. Permeability/flow conductivitycan be defined in terms of Saline Flow Conductivity (SFC), which is ameasure of the ability of a material to transport saline fluid. Anabsorbent polymer is deemed to have desirable permeability properties ifits SFC value is at least about 30×10⁻⁷ cm³ sec/g. A method formeasuring saline flow conductivity is described in U.S. Pat. No.5,562,646 (Goldman et al.) issued Oct. 8, 1996. This method is modifiedto account for gel bed deswelling during the measurement of mixed-bedion-exchange absorbent polymers, as described in the Test Methodssection below. Without being bound by theory, it is believed that duringthe SFC measurement of mixed-bed ion-exchange absorbent polymers, thepolymer sample continues to exchange ions from the saline solution.Ultimately, the ion-exchange capacity of the absorbent polymer isexceeded, and the ionic strength of the solution surrounding the swollenpolymer increases, resulting in some deswelling of the gel bed. Theamount of fluid that is expressed from the gel as a result of thisdeswelling is small compared to the amount of fluid which flows throughthe gel bed during the SFC measurement. Because the final thickness ofthe get bed is significantly less than the initial thickness, the finalthickness of the gel bed is used to calculate SFC values. Using thefinal thickness of the gel bed in the calculation provides the minimumSFC attained during the measurement. Using the initial or anintermediate thickness of the gel bed will provide even higher SFCvalues.

The absorbent polymer compositions of the present invention willpreferably, though not necessarily, have an SFC value of at least about30×10⁻⁷ cm³ sec/g, more preferably at least about 50×10⁻⁷ cm³ sec/g, andstill more preferably at least about 70×10⁻⁷ cm³ sec/g. Typically, theabsorbent polymers of the present invention will have an SFC value fromabout 30 to about 100×10⁻⁷ cm³ sec/g, more typically from about 50 toabout 90×10⁻⁷ cm³ sec/g, and still more typically from about 70 to about80×10⁻⁷ cm³ sec/g.

d. Porosity of the Zone or Layer Comprising Absorbent Polymer

Another important characteristic of the mixed-bed ion-exchange absorbentpolymers of the present invention is the openness or porosity of thezone or layer comprising the absorbent polymers when the polymers areswollen in body fluids under a confining pressure. It is believed thatwhen the absorbent polymers useful herein are present at highconcentrations in an absorbent member or absorbent article and thenswell under usage pressures, the boundaries of the particles come intocontact, and interstitial voids in this high-concentration region becomegenerally bounded by swollen polymer. When this occurs, it is believedthe openness or porosity properties of this region are generallyreflective of the porosity of the zone or layer formed from the swollenabsorbent polymer alone. As used herein, the term “porosity” means thefractional volume (dimensionless) that is not occupied by solidmaterial. See J. M. Coulson et al., Chemical Engineering Vol. 2, 3^(rd)Edition, Pergamon Press, 1978, p. 126.

Porosity is an effective measure of the ability of the zone or layercomprising swollen absorbent polymer to remain open so as to be able toacquire and distribute body fluids under usage pressures. It is believedthat increasing the porosity of swollen high-concentration regions canprovide superior absorption and fluid handling properties for theabsorbent core, thus decreasing incidents of leakage, especially at highfluid loadings. Desirably the porosity of the zone or layer comprisingswollen absorbent polymer approaches or even exceeds the porosity ofconventional acquisition/distribution materials such as wood-pulp fluff.See U.S. Pat. No. 5,562,646, issued Oct. 8, 1996 to Goldman et al.

e. Integrity of the Zone or Layer Comprising Absorbent Polymer

Another important factor which affects the transport of fluid in anabsorbent member is the integrity of the region or regions that comprisethese polymers. Such region or regions having the high concentration ofabsorbent polymer should have sufficient integrity in a partially wetand/or wetted state such that the physical continuity (and thus thecapability of acquiring and transporting fluid into and throughcontiguous interstitial voids/capillaries) of the absorbent member isnot substantially disrupted or altered when subjected to normal useconditions. During normal use, absorbent cores in absorbent articles aretypically subjected to tensional and torsional forces of varyingintensity and direction. These tensional and torsional forces includebunching in the crotch area, stretching and twisting forces as theperson wearing the absorbent article walks, squats, bends, and the like.If wet integrity is inadequate, these tensional and torsional forces canpotentially cause a substantial alteration and/or disruption in thephysical continuity of the absorbent member such that its capability ofacquiring and transporting fluids into and through the contiguous voidsand capillaries is degraded. The layer comprising absorbent polymer canbe partially separated, be fully separated, have gaps introduced, haveareas that are significantly thinned, and/or be broken up into aplurality of significantly smaller segments. Such alteration couldminimize or completely negate any advantageous porosity andpermeability/flow conductivity properties of the absorbent polymer.

Good integrity of the zone or layer comprising absorbent polymer can beachieved according to the present invention by various designs,configurations, compositions, etc., in the absorbent member having thehigh concentration of absorbent polymer, the other components in theabsorbent core (e.g., fluid acquisition members), the other componentsin the absorbent article (e.g., the topsheet and/or backsheet), or anycombination of these components. See U.S. Pat. No. 5,562,646, issuedOct. 8, 1996 to Goldman et al.

In preferred mixed-bed ionic-exchange systems, the cation-exchangecomponent and the anion-exchange component tend to adhere to oneanother. Without being bound by theory, this is believed to be due tothe oppositely charged polyions and or acid/base species at the surfacesof the polymer gel particles which are inherently attracted tooppositely charged species in adjacent particles. This causes athree-dimensional network of adhering polymer particles to beestablished in the zone or layer comprising absorbent polymer, therebygreatly enhancing the integrity of this zone or layer.

The integrity of the region(s) that comprise the polymer compositions ofthe present invention can be measured using the Ball Burst Strength(BBS) Test described below. The ball burst strength is the force (gramsforce) required to rupture a layer of an absorbent polymer compositionthat is swollen in synthetic urine. The absorbent polymer compositionsof the present invention will preferably, though not necessarily, have aBBS value of at least about 50 gf, more preferably at least about 100gf, still more preferably at least about 150 gf and still morepreferably at least about 200 gf. Typically, the BBS values will rangefrom about 50 to about 1000 gf, more typically from about 100 to about800 gf, still more typically from about 150 to about 400 gf and mosttypically from about 200 to about 300 gf.

3. Methods for Making Absorbent Polymers

The absorbent polymers useful in the mixed-bed ion-exchange compositionsof the present invention can be formed by any polymerization and/orcrosslinking techniques. Typical processes for producing these polymersare described in Reissue U.S. Pat. No. 32,649 (Brandt et al.), issuedApr. 19, 1988, U.S. Pat. No. 4,666,983 (Tsubakimoto et al.), issued May19, 1987, and U.S. Pat. No. 4,625,001 (Tsubakimoto et al.), issued Nov.25, 1986, all of which are incorporated by reference.

Polymerization methods to prepare ion-exchange polymers useful in thepresent invention can include free radical, ring-opening, condensation,anionic, cationic, or irradiation techniques. The polymer may beprepared in the neutralized, partially neutralized, or un-neutralizedform, even though the desired product is substantially un-neutralized.The absorbent polymer may be prepared using a homogeneous solutionpolymerization process, or by multi-phase polymerization techniques suchas inverse emulsion or suspension polymerization procedures.

Crosslinking can be effected during polymerization by incorporation ofsuitable crosslinking monomers. Alternatively, the polymers can becrosslinked after polymerization by reaction with a suitable reactivecrosslinking agents. Surface crosslinking of the initially formedpolymers provides absorbent polymers having relatively high PUPcapacity, porosity and permeability. Without being bound by theory, itis believed that surface crosslinking increases the resistance todeformation of the surfaces of swollen absorbent polymer particles, thusreducing the degree of contact between neighboring polymer particleswhen the swollen polymer particles are deformed under an externalpressure. Surface crosslinked absorbent polymers have a higher level ofcrosslinking in the vicinity of the surface than in the interior. Asused herein, “surface” describes the outer-facing boundaries of theparticle. For porous absorbent polymers (e.g., porous particles, etc.),exposed internal boundaries can also be included. By a higher level ofcrosslinking at the surface, it is meant that the level of functionalcrosslinks for the absorbent polymer in the vicinity of the surface isgenerally higher than the level of functional crosslinks for the polymerin the interior. The gradation in crosslinking from surface to interiorcan vary, both in depth and profile.

A number of processes for introducing surface crosslinks are disclosedin the art. Suitable methods for surface crosslinking include thosewhere (i) a di- or poly-functional reagent(s) capable of reacting withexisting functional groups within the absorbent polymer is applied tothe surface of the absorbent polymer; (ii) a di- or poly-functionalreagent that is capable of reacting with other added reagents andpossibly existing functional groups within the absorbent polymer such asto increase the level of crosslinking at the surface is applied to thesurface (e.g., the addition of monomer plus crosslinker and theinitiation of a second polymerization reaction); (iii) no additionalpolyfunctional reagents are added, but additional reaction(s) is inducedamongst existing components within the absorbent polymer either duringor after the primary polymerization process such as to generate a higherlevel of crosslinking at or near the surface (e.g., suspensionpolymerization processes wherein the crosslinker is inherently presentat higher levels near the surface); and (iv) other materials are addedto the surface such as to induce a higher level of crosslinking orotherwise reduce the surface deformability of the resultant swollenpolymer. Suitable general methods for carrying out surface crosslinkingof absorbent polymers according to the present invention are disclosedin U.S. Pat. No. 4,541,871 (Obayashi), issued Sep. 17, 1985; publishedPCT application WO92/16565 (Stanley), published Oct. 1, 1992, publishedPCT application WO90/08789 (Tai), published Aug. 9, 1990; published PCTapplication WO93/05080 (Stanley), published Mar. 18, 1993; U.S. Pat. No.4,824,901 (Alexander), issued Apr. 25, 1989; U.S. Pat. No. 4,789,861(Johnson), issued Jan. 17, 1989; U.S. Pat. No. 4,587,308 (Makita),issued May 6, 1986; U.S. Pat. No. 4,734,478 (Tsubakimoto), issuedMar.29, 1988; U.S. Pat. No. 5,164,459 (Kimura et al.), issued Nov. 17,1992; published German patent application 4,020,780 (Dahmen), publishedAug. 29, 1991; and published European patent application 509,708(Gartner), published Oct. 21, 1992; all of which are incorporated hereinby reference. For cationic absorbent polymers, suitable di- orpoly-functional crosslinking reagents include di/poly-haloalkanes,di/poly-epoxides, di/poly-acid chlorides, di/poly-tosyl alkanes,di/poly-aldehydes, di/poly-acids, and the like.

In general, surface crosslinking may provide absorbent polymercompositions having improved PUP capacity, porosity, and permeability.However, it has been found surprisingly that mixed-bed absorbent polymercompositions wherein the cation-exchange absorbent polymer is preparedwith a relatively high level of crosslinking monomer to yield a materialwith crosslinks distributed uniformly throughout the polymer, haveparticularly desirable improvements in both CUP and PUP capacity,compared to similar compositions having a surface crosslinkedcation-exchange absorbent polymer (See the examples below).

“Without being bound by theory, it is believed that because mixed-bedion-exchange absorbent-polymer compositions imbibe very large quantitiesof fluid, the surfaces of the individual gel particles are susceptibleto disruption upon swelling to many times their original size. Forsurface-crosslinked absorbent polymer compositions, this may lead tosome release of the relatively soft (low modulus) inner core of theparticle which is susceptible to deformation and gel-blocking under thepressures experienced in use, as described above. Homogeneouslycrosslinked absorbent polymer particles have relatively uniform modulusthroughout the particle, and thus may be less susceptible to gelblocking when very highly swollen.”

Homogeneously crosslinked cation-exchange absorbent polymers have anadditional advantage over surface crosslinked cation-exchange absorbentpolymers in that the surface crosslinking step can be eliminated fromthe preparation process. This facilitates preparation of the mixed-bedcompositions from the anion-exchange absorbent polymer and thecation-exchange absorbent polymer components in which the (i) particlesof, e.g., the anion-exchange absorbent polymer contain within smallerdiscontinuous domains of, e.g., the cation-exchange absorbent polymer,or (ii) particles contain bicontinuous domains of both anion- andcation-exchange absorbent polymers. Such morphologies have particularadvantages in providing a close proximity of the anion-exchangeabsorbent polymer and the cation-exchange absorbent polymer in the finalmixed-bed absorbent polymer composition with desirable improvements inthe rate of ion-exchange.

C. Test Methods

1. Performance Under Pressure (PUP) Capacity

This test is based on the method described in U.S. Pat. No. 5,599,335(Goldman et al.) issued Feb. 4, 1997. The test determines the amount ofa synthetic urine solution having a composition and ionic strengthtypical of the urine of young infants absorbed by absorbent polymers(including mixed-bed ion-exchange absorbent polymer compositions) thatare laterally confined in a piston/cylinder assembly under a confiningpressure, e.g. of 0.7 psi or 1.4 psi. The objective of the test is toassess the ability of the absorbent polymer to absorb body fluids over aperiod of time comparable to the duration of use (e.g., overnight) ofarticles comprising the absorbent compositions (e.g., 1, 2, 4, 8, or 16hours), when the polymers arc present at high concentrations in anabsorbent member and exposed to usage pressures. Usage pressures againstwhich absorbent polymer are required to absorb fluid include mechanicalpressures resulting from the weight and/or motions of the wearer,mechanical pressures resulting from elastics and fastening systems, andthe hydrostatic desorption pressures of adjacent layers and/or members.

The test fluid for the PUP capacity test is an aqueous solution preparedby dissolving 2.0 g KCl, 2.0 g Na₂SO₄, 0.85 g NH₄H₂PO₄, 0.15 g(NH₄)₂HPO₄, 0.25 g CaCl₂.2H₂O, and 0.50 g MgCl₂.6H₂O in distilled waterto yield one liter of solution. Such a solution has a composition andionic strength typical of the urine of young infants. This fluid isabsorbed by the absorbent polymers under demand absorption conditions atnear-zero hydrostatic pressure.

A suitable apparatus for this test is shown in FIG. 1. At one end ofthis apparatus is a fluid reservoir 712 (such as a petri dish) having acover 714. Reservoir 712 rests on an analytical balance indicatedgenerally as 716. The other end of apparatus 710 is a fritted funnelindicated generally as 718, a piston/cylinder assembly indicatedgenerally as 720 that fits inside funnel 718, and cylindrical plasticfritted funnel cover indicated generally as 722 that fits over funnel718 and is open at the bottom and closed at the top, the top having apinhole. Apparatus 710 has a system for conveying fluid in eitherdirection that consists of sections glass tubing indicated as 724 and731 a, flexible plastic tubing (e.g., ¼ inch i.d. and ⅜ inch o.d. Tygon®tubing) indicated as 731 b, stopcock assemblies 726 and 738 and Teflon®connectors 748, 750 and 752 to connect glass tubing 724 and 731 a andstopcock assemblies 726 and 738. Stopcock assembly 726 consists of a3-way valve 728, glass capillary tubing 730 and 734 in the main fluidsystem, and a section of glass capillary tubing 732 for replenishingreservoir 712 and foward flushing the fritted disc in fritted funnel718. Stopcock assembly 738 similarly consists of a 3-way valve 740,glass capillary tubing 742 and 746 in the main fluid line, and a sectionof glass capillary tubing 744 that acts as a drain for the system.

Referring to FIG. 1, assembly 720 consists of a cylinder 754, a cup-likepiston indicated by 756 and a weight 758 that fits inside piston 756.Attached to bottom end of cylinder 754 is a No. 400 mesh stainless steelcloth screen 759 that is biaxially stretched to tautness prior toattachment. An absorbent polymer composition indicated generally as 760rests on screen 759. Cylinder 754 is bored from a transparent Lexan® rod(or equivalent) and has an inner diameter of 6.00 cm (area=28.27 cm²),with a wall thickness of approximately 5 mm and a height ofapproximately 5 cm. The piston 756 is in the form of a Teflong or Kel-F®cup and is machined to be a slip fit in cylinder 754 with an annularclearance between the cylinder and the piston of between 0.114 mm and0.191 mm. Cylindrical stainless steel weight 758 is machined to fitsnugly within piston 756 and is fitted with a handle on the top (notshown) for ease in removing. For a confining pressure of 0.7 psi, thecombined weight of piston 756 and weight 758 is 1390 g, whichcorresponds to a pressure of 0.7 psi for an area of 28.27 cm². For aconfining pressure of 1.4 psi, the combined weight of piston 756 andweight 758 is 2780 g.

The components of apparatus 710 are sized such that the flow rate ofsynthetic urine therethrough, under a 10 cm hydrostatic head, is atleast 36 grams per hour per square centimeter of the fritted disc in thefritted funnel 718. Factors particularly impactful on flow rate are thepermeability of the fritted disc in fritted funnel 718 and the innerdiameters of glass tubing 724, 730, 734, 742, 746 and 731 a, andstopcock valves 728 and 740.

Reservoir 712 is positioned on an analytical balance 716 that isaccurate to at least 0.01 g with a drift of less than 0.1 g/hr. Thebalance is preferably interfaced to a computer with software than can(i) monitor balance weight change at pre-set time intervals from theinitiation of the PUP test and (ii) be set to auto initiate dataacquisition upon a weight change of 0.01-0.05 g, depending on balancesensitivity. Tubing 724 entering the reservoir 712 should not contacteither the bottom thereof or cover 714. The volume of fluid (not shown)in reservoir 712 should be sufficient such that air is not drawn intotubing 724 during the measurement. The fluid level in reservoir 712, atthe initiation of the measurement, should be approximately 2 mm belowthe top surface of fritted disc in fritted funnel 718. This can beconfirmed by placing a small drop of fluid on the fritted disc andgravimetrically monitoring the flow of this amount of fluid back intoreservoir 712. This level should not change significantly whenpiston/cylinder assembly 720 is positioned within funnel 718. Thereservoir should have a sufficiently large diameter (e.g., ˜14 cm) sothat withdrawal of ˜40 mL portions results in a change in the fluidheight of less than 3 mm.

Prior to measurement, the assembly is filled with synthetic urinesolution and the fritted disc in fritted funnel 718 is flushed so thatit is filled with fresh synthetic urine solution. To the extentpossible, air bubbles are removed from the bottom surface of the fritteddisc and the system that connects the funnel to the reservoir. Thefollowing procedures are carried out by sequential operation of the3-way stopcocks:

1. Excess fluid on the upper surface of the fritted disc is removed(e.g. poured) from fritted funnel 718.

2. The solution height/weight of reservoir 712 is adjusted to the properlevel/value.

3. Fritted funnel 718 is positioned at the correct height relative toreservoir 712.

4. Fritted funnel 718 is then covered with fritted funnel cover 722.

5. The reservoir 712 and fritted funnel 718 are equilibrated with valves728 and 740 of stopcock assemblies 726 and 738 in the open connectingposition.

6. Valves 728 and 740 are then closed.

7. Valve 740 is then turned so that the funnel is open to the drain tube744.

8. The system is allowed to equilibrate in this position for 5 minutes.

9. Valve 740 is then returned to its closed position.

Steps Nos. 7-9 temporarily “dry” the surface of fritted funnel 718 byexposing it to a small hydrostatic suction of ˜5 cm. This suction isapplied if the open end of tube 744 extends ˜5 cm below the level of thefritted disc in fritted funnel 718 and is filled with synthetic urine.Typically ˜0.2 g of fluid is drained from the system during thisprocedure. This procedure prevents premature absorption of syntheticurine when piston/cylinder assembly 720 is positioned within frittedfunnel 718. The quantity of fluid that drains from the fritted funnel inthis procedure (called the fritted funnel correction weight) is measuredby conducting the PUP test (see below) for a time period of 15 minuteswithout piston/cylinder assembly 720. Essentially all of the fluiddrained from the fritted funnel by this procedure is very quicklyreabsorbed by the frit when the test is initiated. Thus, it is necessaryto subtract this correction weight from weights of fluid removed fromthe reservoir during the PUP test (see below).

The absorbent polymer composition 760 is dried by suitable procedures,for example by desiccation under high vacuum at an appropriatetemperature for a sufficient period of time, so as to reduce the levelof moisture and/or other solvents in the sample as much as possible. Thefinal level of residual moisture, as determined by an appropriatetechnique such as Karl Fischer titration or thermogravimetric analysis,should be less than about 5%, and preferably less than about 3%.Approximately 0.9 g (W_(ap)) of the dried absorbent polymer composition760 (corresponding to a basis weight of 0.032 g/cm²) is added tocylinder 754 and distributed evenly on screen 759. If the absorbentpolymer composition comprises more than one type of particle, theparticles are mixed evenly throughout the composition. Care is taken toprevent absorbent polymer 760 from adhering to the inside walls ofcylinder 754. The piston 756 is slid into cylinder 754 and positioned ontop of the absorbent polymer 760, while ensuring that the piston canslide freely within the cylinder. The piston can be turned gently tohelp distribute the absorbent polymer. The piston/cylinder assembly 720is placed on top of the frit portion of funnel 718, the weight 758 isslipped into piston 756, and the top of funnel 718 is then covered withfritted funnel cover 722. After the balance reading is checked forstability, the test is initiated by opening valves 728 and 740 so as toconnect funnel 718 and reservoir 712. With auto initiation, datacollection commences immediately, as funnel 718 begins to reabsorbfluid.

The weight of fluid remaining in the reservoir 712 is recorded atfrequent intervals for the duration of the test. The PUP capacity at anygiven time, t, is calculated as follows:

PUP capacity (gm/gm; t)=[W _(r)(t=0)−W _(r)(t)−W _(fc) ]/W _(ap)

where W_(r)(t=0) is the weight in grams of reservoir 712 prior toinitiation, W_(r)(t) is the weight in grams of reservoir 712 at theelapsed time t (e.g., 1, 2, 4, 8, or 16 hours), W_(fc) is the frittedfunnel correction weight in grams (measured separately), and W_(ap) isthe initial dry weight in grams of the absorbent polymer.

2. Capacity Under Pressure (CUP)

This test uses essentially the same method and apparatus as the PUPmethod described above. It is intended to be a measure of absorptionperformance for absorbent polymers and absorbent polymer compositions onexposure to a high ionic strength synthetic urine solution having acomposition and ionic strength typical of the urine of older infants andtoddlers The test fluid for the CUP test is an aqueous solution preparedby dissolving 4.0 g KCl, 2.0 g Na₂SO₄, 1.2 g NH₄H₂PO₄, 1.6 g (NH₄)₂HPO₄,0.20 g CaCl₂.2H₂O, 0.55 g MgCl₂.6H₂O, and 7.0 g NaCl in distilled waterto yield one liter of solution. Such a solution has a composition andionic strength typical of the urine of older infants and toddlers. Thisfluid is absorbed by the absorbent polymers under demand absorptionconditions at near-zero hydrostatic pressure.

All other aspects of the CUP test method are the same as those of thePUP test method as described above.

3. Ball Burst Strength (BBS) Test

This test determines the ball burst strength (BBS) of an absorbentpolymer composition. The BBS is the force (peak load, in grams force or“gf”) required to rupture a layer of an absorbent polymer compositionthat is swollen in synthetic urine solution, under procedures specifiedin the test method. BBS is a measure of the integrity of a layer of theabsorbent polymer composition in the swollen state.

A suitable apparatus for BBS measurement is shown in FIG. 7. Thisapparatus comprises an inner cylinder 270 which is used to contain anabsorbent polymer layer 260, an outer cylinder 230, a Teflon®flat-bottomed tray 240, an inner cylinder cover plate 220, and astainless steel weight 210. The inner cylinder 270 is bored from atransparent Lexan® rod or equivalent, and has an inner diameter of 6.00cm (area=28.27 cm²), with a wall thickness of approximately 0.5 cm, anda height of approximately 1.50 cm. The outer-cylinder 230 is bored froma Lexan® rod or equivalent, and has an inner diameter that is slightlylarger than the outer diameter of the inner-cylinder 270, so that theinner-cylinder 270 fits within the outer-cylinder 230 and slides freely.The outer cylinder 230 has a wall thickness of approximately 0.5 cm, anda height of approximately 1.00 cm. The bottom of the outside-cylinder230 is faced with a 400 mesh stainless steel screen 250 that isbiaxially stretched to tautness prior to attachment. The inner cylindercover plate 220 is made of glass plate with a thickness of 0.8 cm and aweight of 500 g. The stainless steel weight 210 has a weight of 1700 g.

A Tensile Tester with a burst test load cell (available fromIntelect-II-STD Tensile Tester, made by Thwing-Albert Instrument Co.,Pennsylvania) is used for this test. Referring to FIG. 8, thisinstrument composes a force sensing load cell 330 equipped with apolished stainless steel ball-shaped probe 290, a moving crosshead 320,a stationary crosshead 310, a circular lower platen 280, and an upperclamping platen 300 that is used to clamp the sample 260 pneumatically.The lower clamp platen 280 is mounted on the stationary crosshead 310.Both lower clamp platen 280 and upper clamp platen 300 have a diameterof 115 mm, a thickness of 2.9 mm, and a circular opening 18.65 mm indiameter. The polished stainless steel ball-shaped probe 290 has adiameter of 15.84 mm. During the BBS test procedure, the movingcrosshead 320 moves up, causing the probe 290 to contact and penetratethe sample 260. When the probe 290 penetrates the sample 260, the testis considered complete, and the appropriate data are recorded.

Referring to the apparatus depicted in FIG. 7, the inner cylinder 270 isinserted into the outside-cylinder 230. A 1.0 g sample of absorbentpolymer composition is added to the inner cylinder 270 and dispersedevenly on the 400 mesh stainless steel screen 250. The assembledcylinders with absorbent polymer are transferred to the Teflon®flat-bottomed tray 240, and inner-cylinder cover plate 220 is positionedonto inner-cylinder 270. A 30.0 mL aliquot of synthetic urine solutionis poured into the Teflon® flat-bottomed tray 240. The synthetic urinesolution passes through the stainless screen and is absorbed by theabsorbent polymer composition 260. The stainless weight 210 is placedonto the inner-cylinder cover plate 220 five minutes after addition ofthe fluid. After an additional 25 minutes, stainless steel weight 210and inner cylinder cover plate 220 are removed. For the procedure to bevalid, all of the synthetic urine solution must be absorbed by theabsorbent polymer composition at this point. The inner-cylinder 270 withthe layer of swollen absorbent polymer 260 is immediately transferred tothe Burst Tester for measurement of the BBS.

Referring to the Burst Tester depicted in FIG. 8, inner-cylinder 270with the swollen absorbent polymer layer 260 is centrally positioned onlower clamp platen 280 and is fixed pneumatically with upper clampingplaten 300. The measurement is performed using a break sensitivity of10.00 g and a test speed of 5.00 inch/minute. The measurement isinitiated and the crosshead 320 moves up until polished stainless steelball-shaped probe 290 penetrates absorbent material gel layer 260. Aftera sample burst is registered, moving crosshead 320 returns to startposition. The BBS is expressed as peak load in grams force. The averageof three determinations is reported as the BBS for the absorbent polymercomposition.

D. Absorbent Members

Absorbent members according to the present invention will comprise thepreviously described mixed-bed ion-exchange absorbent polymercompositions, with or without other optional components such as fibers,thermoplastic material, etc. Preferred materials are described in detailat Col. 23, line 13, through Col. 29, line 16, of U.S. Pat. No.5,562,646 (Goldman et al.). These absorbent members comprising theseabsorbent polymers can function as fluid storage members in theabsorbent core. The principle function of such fluid storage members isto absorb the discharged body fluid either directly or from otherabsorbent members (e.g., fluid acquisition/distribution members), andthen retain such fluid, even when subjected to pressures normallyencountered as a result of the wearer's movements. It should beunderstood, however, that such polymer-containing absorbent members canserve functions other than fluid storage.

In a preferred embodiment, the absorbent members according to thepresent invention will contain one or more regions having a relativelyhigh concentration of these absorbent polymers. In order to providerelatively thin absorbent articles capable of absorbing and retaininglarge quantities of body fluids, it is desirable to maximize the levelof these absorbent polymers and to minimize the level of othercomponents, in particular fibrous components. In order to utilize theseabsorbent polymers at relatively high concentrations, however, it isimportant that these polymers have a relatively high demand absorbencycapacity under a relatively high confining pressure (i.e., PUP capacity)and preferably a relatively high permeability under pressure (i.e.,SFC). This is so that the polymer, when swollen in the presence of bodyfluids, provides adequate capability to acquire these discharged bodyfluids and then transport these fluids through the zone or layer withrelatively high gel concentration to other regions of the absorbentmember and/or absorbent core and/or then to store these body fluids.

In measuring the concentration of mixed-bed ion-exchange absorbentpolymer composition in a given region of an absorbent member, thepercent by weight of the absorbent polymer relative to the combinedweight of absorbent polymer and any other components (e.g., fibers,thermoplastic material, etc.) that are present in the region containingthe polymer is used. With this in mind, the concentration of themixed-bed ion-exchange absorbent polymer composition in a given regionof an absorbent member of the present invention will typically be in therange of from about 40 to 100%, from about 50 to 100%, from about 60 to100%, from about 70 to 100%, from about 80 to 100%, or from about 90% to100%. Of course, in general, the higher the relative concentration ofthe absorbent polymer, the thinner and less bulky the absorbent member.

E. Absorbent Cores and Absorbent Articles

The mixed-bed ion-exchange absorbent polymer compositions of the presentinvention can be used just as conventional absorbent polymers in anyabsorbent core and/or absorbent article used for the absorption of bodyfluids, as described in U.S. Pat. No. 5,562,646 (Goldman et al.). The'646 patent describes absorbent cores in detail at Col. 33, line 7,through Col. 52, line 24; and describes absorbent articles in detail atCol. 52, line 25, through Col. 54, line 9. Such articles includediapers, catamenial products and/or adult incontinence products.Substitution of mixed-bed ion-exchange absorbent polymers for theconventional absorbent polymers at the same weight will allow forincreased absorbent capacity of the article. Alternatively, themixed-bed ion-exchange absorbent polymers can be substituted at a lowerweight so as not to increase the absorbent capacity of the article, butto allow for a lighter, thinner, and/or less bulky article.

Incorporation of mixed-bed ion-exchange absorbent polymers in anypreviously disclosed absorbent articles is obvious to one skilled in theart. Such products include those with features, for example, such asbreathable backsheets, hook-and-loop fasteners, bicomponent fibermatrices, and the like.

Absorbent articles which may contain mixed-bed ion-exchange absorbentpolymer compositions described herein are disclosed, for example, inU.S. Pat. No. 3,224,926 (Bemardin), issued Dec. 21, 1965; U.S. Pat. No.3,440,135 (Chung), issued Apr. 22, 1969; U.S. Pat. No. 3,932,209(Chatterjee), issued Jan. 13, 1976; and U.S. Pat. No. 4,035,147(Sangenis et al.), issued Jul. 12, 1977. More preferred stiffened fibersare disclosed in U.S. Pat. No. 4,822,453 (Dean et al.), issued Apr. 18,1989; U.S. Pat. No. 4,888,093 (Dean et al.), issued Dec. 19, 1989; U.S.Pat. No. 4,898,642 (Moore et al.), issued Feb. 6, 1990; and U.S. Pat.No. 5,137,537 (Herrow et al.), issued Aug. 11, 1992; U.S. Pat. No.4,818,598 (Wong) issued Apr. 4, 1989; U.S. Pat. No. 5,562,646, (Goldmanet al.) issued Oct. 8, 1996; U.S. Pat. No. 5,217,445 (Young et al.),issued Jun. 8, 1993; U.S. Pat. No. 5,360,420, (Cook et al.), issued Nov.1, 1994; U.S. Pat. No. 4,935,022 (Lash et al.); U.S. applications Ser.No. 08/153,739 (Dragoo et al.), filed Nov. 16, 1993; U.S applicationSer. No. 08/164,049 (Dragoo et al.), filed Dec. 8, 1993; U.S. Pat. No.4,260,443 (Lindsay et al.); U.S. Pat. No. 4,467,012 (Pedersen et al.),issued Aug. 21, 1984; U.S. Pat. No. 4,715,918 (Lang), issued Dec. 29,1987; U.S. Pat. No. 4,851,069 (Packard et al.), issued Jul. 25, 1989;U.S. Pat. No. 4,950,264 (Osborn), issued Aug. 21, 1990; U.S. Pat. No.4,994,037 (Bernardin), issued Feb. 19, 1991; U.S. Pat. No. 5,009,650(Bernardin), issued Apr. 23, 1991; U.S. Pat. No. 5,009,653 (Osbom),issued Apr. 23, 1991; U.S. Pat. No. 5,128,082 (Makoui), Jul. 7, 1992;U.S. Pat. No. 5,149,335 (Kellenberger et al.), issued Sep. 22, 1992; andU.S. Pat. No. 5,176,668 (Bernardin),issued Jan. 5, 1993; U.S.application Ser. No. 141,156 (Richards et al.), filed Oct. 21, 1993;U.S. Pat. No. 4,429,001 (Kolpin et al.), issued Jan. 31, 1984; U.S.patent application Ser. No. 07/794,745, (Aziz et al.) filed on Nov. 19,1991; all of which are incorporated by reference.

F. SPECIFIC EXAMPLES

A lightly crosslinked, partially-neutralized poly(acrylic acid)absorbent polymer with a relatively high PUP capacity (˜33 g/g at 0.7psi; 60 minutes) is obtained from the Chemdal Corporation of Palantine,Illinois (ASAP-2300; lot no. 426152). (Similar samples of ASAP-2300 areavailable from The Procter & Gamble Co., Paper Technology Division,Cincinnati, Ohio.) This material serves as a control sample and isdesignated herein as “Control Sample”.

A sample of an absorbent polymer that provides increased integrityrelative to conventional polyacrylate absorbent polymers is obtainedfrom Nippon Shokubai (Lot # TN37408). This is a polyacrylate that issurface-treated with polyethylenimine. The polymer is described indetail in U.S. Pat. No. 5,382,610, filed Jan. 17, 1995. This material isreferred to herein as “Sample ST”.

Example 1

Preparation of Ion-Exchange Absorbent Polymers

(i) Cation-Exchange Absorbent Polymer

To prepare the cation-exchange absorbent polymer, a portion of theControl Sample is sieved with a U.S.A. Series Standard 50 mesh sieve toremove particles that are larger than about 300 microns in diameter.About 50 grams of the sieved absorbent polymer, with particle sizesmaller than about 300 microns, is converted to the acid form bysuspending the polymer in a dilute hydrochloric acid solution which isprepared by adding about 46.5 g concentrated HCl (Baker; 36.5-38% HCl)to about 900 mL distilled deionized water. The suspension is stirredgently for about 1.5 hours, after which the absorbent polymer is allowedto settle, and the supernatant fluid is removed by decantation. Thedecanted liquid is replaced by an equal volume of distilled deionizedwater, the suspension is shaken gently for approximately one hour, theabsorbent polymer is allowed to settle, and the supernatant fluid isagain removed by decantation. This exchange process is repeated (abouteight times) with an equal volume of distilled deionized water until thepH of the supernatant liquid reaches 5-6. The exchange process is thenrepeated three times with isopropanol (reagent grade; VWR, West Chester,Pa.), three times with acetone (reagent grade; VWR), and once withanhydrous ether (reagent grade; EM Science, Gibbstown, N.J.). Theproduct is spread out gently on a sheet of polytctrafluoroethylene andallowed to dry overnight. After gentle manual disruption with a spatula,the product is dried under high vacuum for 96 hours at room temperatureto remove any residual solvents. The sample is sieved through a U.S.A.20 mesh sieve to remove any large particles or agglomerates.Approximately 30 grams of acid-form, crosslinked poly(acrylic acid),ion-exchange absorbent polymer is obtained and stored under a dryatmosphere (Sample PAA).

(ii) Anion-Exchange Absorbent Polymer

Branched polyethylenimine with a nominal weight average molecular weightof 750,000 g/mole is obtained as a 50% aqueous solution from AldrichChemical Co., Milwaukee, Wis. (catalog number 18,917-8; lot number12922PQ). A 20 gram sample of this solution is further diluted with 37grams of distilled water and is stirred for 30 minutes in a 250 mLbeaker to achieve complete dissolution. Ethylene glycol diglycidyl ether(50% soln.), 2.14 grams (Aldrich Chemical Co., catalog number, E2,720-3;lot number, 07405DN), is added to the polyethylenimine solution and themixture is stirred at room temperature for approximately two minutesbefore being placed in a vented oven at approximately 65° C. for threehours. The resultant gel is allowed to cool and then broken into piecesapproximately 1 to 5 mm in diameter. The mixture is then transferred toa 4000 mL beaker containing two liters of distilled water and stirredgently overnight. The excess water is decanted off and the remainingsample is dried under high vacuum for approximately 96 hours to yield alightly crosslinked polyethylenimine anion-exchange absorbent polymerwhich is stored under a dry atmosphere (Sample BPEI).

(iii) Mixed-Bed Ion-Exchange Absorbent Polymer

The crosslinked polyethylenimine anion-exchange absorbent polymer(Sample BPEI) is cryogenically ground and sieved under an atmosphere ofdry nitrogen. A particle size fraction is collected which passes througha U.S.A. Series Standard 25 mesh sieve, but not through a U.S.A. SeriesStandard 70 mesh sieve (i.e. a fraction with particles in the range ofapproximately 200 to 700 microns in diameter).

Approximately equal weights of the sieved crosslinked poly(acrylic acid)cation-exchange absorbent polymer (Sample PAA) and the sievedcrosslinked polyethylenimine anion-exchange absorbent polymer (SampleBPEI) are mixed together so as to distribute the particles of each typeof polymer evenly throughout the mixture. This mixture comprises amixed-bed ion-exchange absorbent polymer composition (Sample MB-1) ofthe present invention.

(iv) PUP Capacity Measurements

Approximately 0.9 grams of the mixed-bed ion-exchange absorbent polymercomposition (Sample MB-1 ) is transferred to a PUP cylinder (asdescribed in the Test Methods section above), and gently spread out overthe entire area of the screen comprising the base of the cylinder. PUPcapacities are determined on separate samples under confining pressuresof 0.7 and 1.4 psi, with the amount of fluid absorbed measured atfrequent intervals for a period of 16 hours. The measured PUP capacitiesat 0.7 and 1.4 psi are shown as a function of time in FIGS. 3 and 4,respectively. Selected PUP capacity data at 2, 4, 8 and 16 hours arelisted in Table 1 below.

TABLE 1 PUP Capacities for Mixed-bed Ion-exchange Absorbent PolymerCompositions 0.7 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi 1.4 psi (4 hrs) (8hrs) (16 hrs) (2 hrs) (8 hrs) (16 hrs) Sample MB-1 44 g/g 48 g/g 50 g/g32 g/g 40 g/g 42 g/g Control Sample 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g20 g/g

A comparison of the PUP capacities indicates that the mixed-bedion-exchange absorbent polymer composition (Sample MB-1) exhibits anapproximately 100% increase in PUP capacity at a confining pressure of1.4 psi, and an approximately 40% increase in PUP capacity at aconfining pressure of 0.7 psi after 8 hours, relative to the capacitiesof the partially neutralized polyacrylate absorbent polymer underanalogous test conditions (Control Sample).

(v) CUP Measurements

Approximately 0.9 grams of the mixed-bed ion-exchange absorbent polymercomposition (Sample MB-1) is transferred to a CUP cylinder (as describedin the Test Methods section above), and gently spread out over theentire area of the screen comprising the base of the cylinder. CUPmeasurements are determined on separate samples under confiningpressures of 0.7 and 1.4 psi, with the amount of fluid absorbed measuredat frequent intervals for a period of 16 hours. Selected CUP data at 1,2, 4, 8 and 16 hours are listed in Table 2 below.

TABLE 2 CUP data for Mixed-bed Ion-exchange Absorbent PolymerCompositions 0.7 psi 0.7 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi 1.4 psi 1.4psi (1 hr) (4 hrs) (8 hrs) (16 hrs) (1 hr) (2 hrs) (8 hrs) (16 hrs)Sample MB-1 17 g/g 20 g/g 21 g/g 22 g/g 15 g/g 18 g/g 21 g/g 22 g/gControl Sample 21 g/g 21 g/g 22 g/g 22 g/g 13 g/g 13 g/g 15 g/g 17 g/g

A comparison of the CUP indicates that the mixed-bed ion-exchangeabsorbent polymer composition (Sample MB-1) absorbs significantly higherfluid at a confining pressure of 1.4 psi relative to the capacities ofthe partially neutralized polyacrylate absorbent polymer under analogoustest conditions (Control Sample).

(vi) Permeability Measurement

A measure of permeability and an indication of porosity is provided bythe saline flow conductivity of the gel bed as described in U.S. Pat.No. 5,562,646, (Goldman et al.) issued Oct. 8, 1996. This method ismodified for mixed-bed ion-exchange absorbent polymer systems, asdiscussed below. Approximately 0.9 grams of the mixed-bed ion-exchangeabsorbent polymer composition (Sample MB-1) is transferred to a cylinderdesigned for Saline Flow Conductivity measurement (SFC), and is gentlyspread out over the entire area of the screen comprising the base of thecylinder. The measured saline flow conductivity values are listed inTable 3 below.

TABLE 3 SFC Values for Mixed-bed Ion-exchange Absorbent PolymerCompositions SFC Value Sample MB-1 ˜68 × 10⁻⁷ cm³ · sec/g Control Sample˜10 × 10⁻⁷ cm³ · sec/g

Comparison of the saline flow conductivity values demonstrate that thepermeability of the mixed-bed ion-exchange absorbent polymer composition(Sample MB-1) is substantially greater than that of the partiallyneutralized polyacrylate absorbent polymer (Control Sample) underanalogous test conditions. It is believed that the mixed-bedion-exchange absorbent polymer sample continues to exchange ions fromthe saline solution during the SFC measurement. Ultimately, theion-exchange capacity of the absorbent polymer is exceeded, and theionic strength of the solution surrounding the swollen polymerincreases, resulting in some deswelling of the gel bed. The amount offluid that is expressed from the gel as a result of this deswelling issmall compared to the amount of fluid which flows through the gel bedduring the SFC measurement. Because the final thickness of the gel bedis significantly less than the initial thickness, the final thickness ofthe gel bed is used to calculate SFC values. Using the final thicknessof the gel bed in the calculation provides the minimum SFC attainedduring the measurement. Using the initial or an intermediate thicknessof the gel bed will provide even higher SFC values.

Although SFC is not a direct measure of porosity, high permeability tofluid also generally requires a high degree of porosity in particulateabsorbent polymer systems. Thus, the relatively high SFC value for themixed-bed ion-exchange absorbent polymer composition also denotes arelatively high level of porosity.

(vi) Integrity of the Gel Bed

A measure of the integrity of a layer of the absorbent polymercomposition in the swollen state is provided by ball burst strength(BBS) as described previously. The measured ball burst strength valuesfor Sample MB-1, Sample ST, and Control Sample are listed in Table 4below:

TABLE 4 BBS Values for Mixed-bed Ion-exchange Absorbent PolymerCompositions BBS Sample MB-1 225 gf Sample ST 133 gf Control Sample  17gf

A comparison of the ball burst strength values in Table 3 indicate thatthe mixed-bed ion-exchange absorbent polymer composition (Sample MB-1)exhibits a substantial increase in the integrity of the gel layerrelative to the partially neutralized polyacrylate absorbent polymer(Control Sample) and Sample ST, under analogous test conditions.

Example 2

Preparation of Ion-Exchange Absorbent Polymers

(i) Cation-Exchange Absorbent Polymer

The cation exchange absorbent polymer is prepared as described inExample 1, Section (i); (Sample PAA).

(ii) Anion-Exchange Absorbent Polymer

a) Preparation of Crosslinked Polyallylamine

Polyallylamine hydrochloride with a nominal weight average molecularweight of 60,000 g/mole is obtained from Polysciences, Inc. Warrington,Pa. (catalog number 18378; lot number 455913). A solution ofpolyallylamine hydrochloride is prepared by dissolving 16.4 grams of thepolymer in 165 mL distilled water. 15.6 grams of a 50% aqueous sodiumhydroxide solution are added dropwise to this solution while stirring.Ethylene glycol diglycidyl ether (50% soln.), 2.0 grams (AldrichChemical Co., catalog number, E2,720-3; lot number, 07405DN), is addedto the polyallylamine solution and the mixture is stirred at roomtemperature for approximately two minutes before being placed in avented oven at approximately 65° C. for three hours. The resultant gelis broken into pieces approximately 5 mm in diameter, and transferred toa 4000 mL beaker containing one liter of distilled water. The mixture isstirred gently overnight and the excess water is decanted off. Theremaining sample is dried under high vacuum at room temperature forapproximately 96 hours to yield a lightly crosslinked polyallylamineanion-exchange absorbent polymer which is stored under a dry atmosphere(Sample PAAM).

b) Methylation of Sample PAAM

Formic acid (96% soln.), 21.02 grams (Aldrich Chemical Co., catalognumber 25,136-4), and formaldehyde (37% soln.), 35.56 grams (AldrichChemical Co., catalog number 25,254-9; lot number, 04717TZ), are addedto 800 grams of distilled water. Ten grams of crosslinked polyallylamine(Sample PAAM) are added to the above solution and the mixture is placedin an oven at 70° C. for 24 hours. The gel is recovered by decantation,and stirred overnight in 1000 mL water to remove extractables. Thesupernatant solution is decanted off and replaced with 1 liter of 1.7%aqueous sodium hydroxide solution to remove excess formic acid in thegel. The mixture is allowed to stand for approximately 24 hours and thepolymer is recovered by decantation of the supernatant fluid. Thisprocess is repeated (about three times) with 1 liter of 1.7% aqueoussodium hydroxide solution until a pH of 13 is obtained. The gel isrecovered by vacuum filtration and soaked in 3000 mL of water overnight.The excess water is decanted off and the remaining sample is dried underhigh vacuum at room temperature for approximately 96 hours to yield alightly crosslinked tertiary-polyallylamine anion-exchange absorbentpolymer which is stored under a dry atmosphere. NMR spectroscopicanalysis of the product indicates that approximately 90 percent of theamine groups in the polymer are methylated to form tertiary aminemoieties (Sample t-PAAM).

(iii) Mixed-Bed Ion-Exchange Absorbent Polymer

The crosslinked tertiary-polyallylamine anion-exchange absorbent polymer(Sample t-PAAM) is cryogenically ground and sieved under an atmosphereof dry nitrogen. A particle size fraction is collected which passesthrough a U.S.A. Series Standard 25 mesh sieve, but not through a U.S.A.Series Standard 70 mesh sieve (i.e. a fraction with particles in therange of approximately 200 to 700 microns in diameter).

Approximately 0.29 grams of the sieved crosslinked poly(acrylic acid)cation-exchange absorbent polymer (Sample PAA) and 0.71 grams of thesieved crosslinked tertiary-polyallylamine anion-exchange absorbentpolymer (Sample t-PAAM) are mixed together so as to distribute theparticles of each type of polymer evenly throughout the mixture. Thismixture comprises a mixed-bed ion-exchange absorbent polymer composition(Sample MB-2 of the present invention).

(iv) PUP Capacity Measurements

Approximately 0.9 grams of the mixed-bed ion-exchange absorbent polymercomposition (Sample MB-2) is transferred to a PUP cylinder (as describedin the Test Methods section above), and gently spread out over theentire area of the screen comprising the base of the cylinder. PUPcapacities are determined on separate samples under confining pressuresof 0.7 and 1.4 psi, with the amount of fluid absorbed measured atfrequent intervals for a period of 16 hours. The measured PUP capacitiesat 0.7 and 1.4 psi are shown as a function of time in FIGS. 3 and 4,respectively. Selected PUP capacity data at 2, 4, 8 and 16 hours arelisted in Table 5 below.

TABLE 5 PUP Capacities for Mixed-bed Ion-exchange Absorbent PolymerCompositions 0.7 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi 1.4 psi (4 hrs) (8hrs) (16 hrs) (2 hrs) (8 hrs) (16 hrs) Sample MB-2 41 g/g 43 g/g 44 g/g33 g/g 40 g/g 42 g/g Control Sample 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g20 g/g

A comparison of the PUP capacities indicates that the mixed-bedion-exchange absorbent polymer composition (Sample MB-2) absorbssubstantially more synthetic urine solution than the partiallyneutralized polyacrylate absorbent polymer (Control Sample) under thetest conditions described above.

Example 3

Preparation of Ion-Exchange Absorbent Polymers

(i) Cation-Exchange Absorbent Polymer

The cation exchange absorbent polymer is prepared as described inExample 1 Section (i); (Sample PAA).

(ii) Anion-Exchange Absorbent Polymer

a) Preparation of Linear Polyethylenimine

Poly(2-ethyl-2-oxazoline) with a nominal weight average molecular weightof 500,000 g/mole is obtained from Aldrich Chemical Co., Milwaukee, Wis.(catalog number 37, 397-4; lot number 17223HG). A 100 gram sample ofpoly(2-ethyl-2-oxazoline) is dissolved in a hydrochloric acid solutionwhich is prepared by mixing 1000 mL water and 200 mL concentratedhydrochloric acid. The solution is refluxed at 100° C. for 72 hours thenallowed to cool to room temperature. Product is precipitated from thereaction solution by adding 256 mL of a 50% solution of sodium hydroxidedropwise while stirring. The white solid precipitate is recovered byvacuum filtration and washed with 5000 mL of water. The product is driedunder high vacuum for 48 hours to yield linear polyethylenimine.

b) Preparation of Crosslinked Linear Polyethylenimine

Linear polyethylenimine, 5.0 g, as prepared above, is dissolved in 50 mLof methanol. Ethylene glycol diglycidyl ether (50% soln.), 0.5 grams(Aldrich Chemical Co., catalog number E2,720-3; lot number, 07405DN), isadded to the linear polyethylenimine solution and the mixture is stirredat room temperature for approximately two minutes before being placed ina vented oven at approximately 65° C. for three hours. The resultant gelis broken into particles approximately 5 mm in diameter, and is stirredgently in 500 mL of methanol overnight. The sample is recovered bydecantation, and is dried under high vacuum for approximately 48 hoursto yield a lightly crosslinked polyethylenimine anion-exchange absorbentpolymer which is stored under a dry atmosphere (Sample LPEI-1).

c) Partial Methylation of Crosslinked Polyetliyleniminc

Linear polyethylenimine, 5.37 g, as prepared above, is dissolved in 45grams of methanol. Ethylene glycol diglycidyl ether (50% soln.), 1.07grams (Aldrich Chemical Co., catalog number E2,720-3; lot number,07405DN), is added to the linear polyethylenimine solution and themixture is stirred at room temperature for approximately two minutesbefore being placed in a vented oven at approximately 65° C. for threehours. The resultant gel is broken into particles approximately 5 mm indiameter, and is stirred gently in 500 mL of methanol overnight. Thesample is recovered by decantation, and is dried under high vacuum forapproximately 48 hours to yield a lightly crosslinked polyethylenimineanion-exchange absorbent polymer which is stored under a dry atmosphere(Sample LPEI-2).

Formic acid (96% soln.), 48.44 grams (Aldrich Chemical Co., catalognumber 25,136-4), and formaldehyde (37% soln.), 81.17 grams (AldrichChemical Co., catalog number 25,254-9), are added to 370.39 grams ofdistilled water to yield 500 grams of stock solution. 46.98 grams ofthis stock solution are added to 5.37 grams of crosslinked linearpolyethylenimine (Sample LPEI-2). The mixture is further diluted with450 mL of distilled water and placed in an oven at 70° C. for 24 hours.The gel is recovered by decantation, and stirred overnight in 2500 mLwater to remove extractables. The supernatant solution is decanted offand replaced with 20 mL of 50% aqueous sodium hydroxide solution toremove excess formic acid in the gel. The mixture is allowed to standfor approximately 3 hours and the polymer is recovered by decanting thesupernatant fluid. This process is repeated (about three times) with 20mL of 50% aqueous sodium hydroxide solution until a pH of 13 isobtained. The gel is recovered by vacuum filtration and soaked in 1000mL of water overnight. The supernatant fluid is decanted off andreplaced with 500 mL of tetrahydrofuran. After 24 hours, thetetrahydrofiran is decanted off and replaced by 500 mL of anhydrousether. After 24 hours, the ether is decanted off and the gel is driedunder high vacuum at room temperature for 48 hours. NMR spectroscopicanalysis of the product indicates that approximately 65 percent of theamine groups in the polymer are methylated to form tertiary aminemoieties. (Sample NMEI-65).

(iii) Mixed-Bed Ion-Exchange Absorbent Polymer

The crosslinked linear polyethylenimine and poly(N-methylethylenimine)anion-exchange absorbent polymers (Samples LPEI-1 and NMEI-65) are eachseparately cryogenically ground and sieved under an atmosphere of drynitrogen. For each material, a particle size fraction is collected whichpasses through a U.S.A. Series Standard 25 mesh sieve, but not through aU.S.A. Series Standard 70 mesh sieve (i.e. a fraction with particles inthe range of approximately 200 to 700 microns in diameter).

Approximately one gram of each of the sieved crosslinked anion-exchangeabsorbent polymers (Samples LPEI-1 and NMEI-65) are separately mixedwith one gram portions of the sieved crosslinked poly(acrylic acid)cation-exchange absorbent polymer (Sample PAA) so as to distribute theparticles of each type of polymer evenly throughout the mixtures. Thesemixtures each comprise a mixed-bed ion-exchange absorbent polymercomposition (Samples MB-3a and MB-3b, respectively) of the presentinvention.

(iv) PUP Capacity Measurements

Approximately 0.9 grams of the mixed-bed ion-exchange absorbent polymercompositions (Sample MB-3a, and MB-3b) are transferred to separate PUPcylinders (as described in the Test Methods section above), and gentlyspread out over the entire area of the screen comprising the base of thecylinder. PUP capacities are determined on separate samples underconfining pressures of 0.7 and 1.4 psi, with the amount of fluidabsorbed measured at frequent intervals for a period of 16 hours. Themeasured PUP capacities at 0.7 and 1.4 psi are shown as a function oftime in FIGS. 3 and 4, respectively. Selected PUP capacity data at 4, 8and 16 hours are listed in Table 6 below.

TABLE 6 PUP Capacities for Mixed-bed Ion-exchange Absorbent PolymerCompositions 0.7 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi (4 hrs) (8 hrs) (16hrs) (8 hrs) (16 hrs) Sample MB-3a — — — 32 g/g 37 g/g Sample MB-3b 39g/g 42 g/g 43 g/g — — Control Sample 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g

A comparison of the PUP capacities indicates that the mixed-bedion-exchange absorbent polymer compositions (Sample MB-3a and MB-3b)absorb substantially more synthetic urine solution than the partiallyneutralized polyacrylate absorbent polymer (Control Sample) under thetest conditions described above.

Example 4

Preparation of Ion-Exchange Absorbent Polymers

(i) Cation-Exchange Absorbent Polymer

Preparation of Crosslinked Polyacrylic acid

A homogeneously crosslinked polyacrylic acid is synthesized by placing450 grams of acrylic acid monomer (Aldrich Chemical Co., Milwaukee,Wis., catalog number 14,723-0; lot number 15930CS) in a clean 4000 mLresin kettle. 7.2 grams of N,N′-methylenebisacrylamide (Aldrich ChemicalCo., catalog number 14,607-2; lot number 04511DR) and 0.85 grams of2,2′-Azobis(2-amidinopropane) dihydrochloride (Wako, lot number P2197)are dissolved in 2050 grams of distilled water and added to the acrylicacid monomer in the resin kettle. The solution is sparged with nitrogenfor 15 minutes to remove dissolved oxygen. The resin kettle is thensealed and the solution is heated at 40° C. for 16 hours.

The resultant gel is allowed to cool and then broken into piecesapproximately 1 cm in diameter and dried in a vacuum oven at 55° C. for60 hours. The sample is ground using a Wiley Mill and is sieved througha U.S.A. 20 mesh sieve to obtain homogeneously crosslinked polyacrylicacid (Sample PAA-2).

(ii) Anion-Exchange Absorbent Polymer

Preparation of Crosslinked Polyallylamine

Polyallylamine (PAA-H), 1250 grams of 20% solution (Nitto Boseki Co.,LTD, Tokyo, Japan, lot number 80728) is weighed into a 2000 mL glassjar. Ethylene glycol diglycidyl ether, 19 grams of 50% solution (AldrichChemical Co., catalog number, E2,720-3) is diluted with 20 grams ofdistilled water and added to the polyallylamine solution. The mixture isstirred at room temperature for approximately two minutes before beingplaced in a vented oven at approximately 60° C. overnight.

The resultant gel is broken into pieces approximately 5 mm in diameterand dried under high vacuum for approximately 96 hours to yield alightly crosslinked polyallylamine anion-exchange absorbent polymerwhich is stored under a dry atmosphere (Sample PAAM-2).

(iii) Mixed-Bed Ion-Exchange Absorbent Polymer

The crosslinked polyallylamine anion-exchange absorbent polymer (SamplePAAM-2) is ground and sieved. A particle size fraction is collectedwhich passes through a U.S.A. Series Standard 25 mesh sieve, but notthrough a U.S.A. Series Standard 70 mesh sieve (i.e. a fraction withparticles in the range of approximately 200 to 700 microns in diameter).

Approximately 125 grams of the sieved crosslinked polyacrylic acid (200to 700 microns diameter) cation-exchange absorbent polymer (SamplePAA-2) and 125 grams of the sieved crosslinked polyallylamineanion-exchange absorbent polymer (Sample PAAM-2) are mixed together soas to distribute the particles of each type of polymer evenly throughoutthe mixture. This mixture comprises a mixed-bed ion-exchange absorbentpolymer composition (Sample MB-4 of the present invention).

(iv) PUP Capacity Measurements

Approximately 0.9 grams of the mixed-bed ion-exchange absorbent polymercomposition (Sample MB-4) are transferred to a PUP cylinder (asdescribed in the Test Methods section above), and gently spread out overthe entire area of the screen comprising the base of the cylinder. PUPcapacities arc determined on separate samples under confining pressuresof 0.7 and 1.4 psi, with the amount of fluid absorbed measured atfrequent intervals for a period of 16 hours. Selected PUP capacity dataat 2, 4, 8 and 16 hours are listed in Table 7 below.

TABLE 7 PUP Capacities for Mixed-bed Ion-exchange Absorbent PolymerCompositions 0.7 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi 1.4 psi (4 hrs) (8hrs) (16 hrs) (2 hrs) (8 hrs) (16 hrs) Sample MB-4 53 g/g 56 g/g 59 g/g38 g/g 50 g/g 55 g/g Control Sample 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g20 g/g

A comparison of the PUP capacities indicates that the mixed-bedion-exchange absorbent polymer composition (Sample MB-4) absorbssubstantially more synthetic urine solution than the partiallyneutralized polyacrylate absorbent polymer (Control Sample) under thetest conditions described above.

(v) CUP Measurements

Approximately 0.9 grams of the mixed-Led ion-exchange absorbent polymercomposition (Sample MB-4) are transferred to a CUP cylinder (asdescribed in the Test Methods section above), and gently spread out overthe entire area of the screen comprising the base of the cylinder. CUPmeasurements are determined on separate samples under confiningpressures of 0.7 and 1.4 psi, with the amount of fluid absorbed measuredat frequent intervals for a period of 16 hours. The measured CUP at 0.7and 1.4 psi are shown as a function of time in FIGS. 5 and 6,respectively. Selected CUP data at 1, 2, 4, 8 and 16 hours are listed inTable 8 below.

TABLE 8 CUP data for Mixed-bed Ion-exchange Absorbent PolymerCompositions 0.7 psi 0.7 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi 1.4 psi 1.4psi (1 hr) (4 hrs) (8 hrs) (16 hrs) (1 hr) (2 hrs) (8 hrs) (16 hrs)Sample MB-4 23 g/g 28 g/g 29 g/g 29 g/g 19 g/g 23 g/g 28 g/g 29 g/gControl Sample 21 g/g 21 g/g 22 g/g 22 g/g 13 g/g 13 g/g 15 g/g 17 g/g

A comparison of the CUP data indicates that the mixed-bed ion-exchangeabsorbent polymer composition (Sample MB-4) absorbs substantially morehigh ionic strength synthetic urine solution than the partiallyneutralized polyacrylate absorbent polymer (Control Sample) under thetest conditions described above.

Example 5

Preparation of Ion-Exchange Absorbent Polymers

(i) Cation-Exchange Absorbent Polymer

Preparation of Crosslinked Polyacrylic Acid

A homogeneously crosslinked polyacrylic acid is synthesized by placing40.45 grams of acrylic acid monomer (Aldrich Chemical Co.., catalognumber 14,723-0; lot number 15930CS) in a clean 500 mL resin kettle.0.65 grams of N,N′-methylenebisacrylamide (Aldrich Chemical Co., catalognumber 14,607-2; lot number 04512 DR) and 0.076 grams of2,2′-Azobis(2-amidinopropane) dihydrochloride (Wako, lot number P2197)are dissolved in 200 grams of water and added to the acrylic acidmonomer in the resin kettle. The solution is sparged with nitrogen for15 minutes to remove dissolved oxygen. The resin kettle is then sealedand the solution is heated at 40° C. for 16 hours to yield a lightlycrosslinked polyacrylic acid cation-exchange absorbent polymer gel(Sample PAA-3).

(ii) Anion-Exchange Absorbent Polymer

Preparation of Crosslinked Polyallylamine

Polyallylamine (PAA-H), 202 grams of 20% solution (Nitto Boseki Co.,LTD, Tokyo, Japan, lot number 80728) is weighed into a 500 mL glass jar.Ethylene glycol diglycidyl ether, 3.0 grams of 50% solution (AldrichChemical Co., catalog number, E2,720-3) is added to the polyallylaminesolution. The mixture is stirred at room temperature for approximatelytwo minutes before being placed in a vented oven at approximately 60° C.for two hours to yield a lightly crosslinked polyallylamineanion-exchange absorbent polymer gel (Sample PAAM-3).

(iii) Mixed-Bed Ion-Exchange Absorbent Polymer

Approximately 20 grams of the crosslinked polyallylamine anion-exchangeabsorbent polymer gel (Sample PAAM-3) and approximately 20 grams of thecrosslinked polyacrylic acid cation-exchange absorbent polymer gel(Sample PAA-3) are placed in an Osterizer blender (Model # 855-08K). Thecation-exchange and anion-exchange absorbent polymer gels are blended inthe blender at high speed, assuring that the gels are well blended (e.g.scraping the sides of the blender to be sure all material reaches themixing zone) for a total of 1.5 minutes. The resultant cation-exchangeand anion-exchange absorbent polymer blend is dried under high vacuumfor approximately 96 hours. The cation-exchange and anion-exchangeabsorbent polymer blend is ground and sieved. A particle size fractionis collected which passes through a U.S.A. Series Standard 25 meshsieve, but not through a U.S.A. Series Standard 70 mesh sieve (i.e. afraction with particles in the range of approximately 200 to 700 micronsin diameter) to yield a mixed-bed ion-exchange absorbent polymercomposition. The resultant particle contains bicontinuous domains ofboth anion- and cation-exchange absorbent polymers (Sample MB-5 of thepresent invention).

(iv) PUP Capacity Measurements

Approximately 0.9 grams of the mixed-bed ion-exchange absorbent polymercomposition (Sample MB-5) are transferred to a CUP cylinder (asdescribed in the Test Methods section above), and gently spread out overthe entire area of the screen comprising the base of the cylinder. PUPcapacities are determined on separate samples under confining pressuresof 0.7 and 1.4 psi, with the amount of fluid absorbed measured atfrequent intervals for a period of 16 hours. Selected PUP capacity dataat 2, 4, 8 and 16 hours are listed in Table 9 below.

TABLE 9 PUP Capacities for Mixed-bed Ion-exchange Absorbent PolymerCompositions 0.7 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi 1.4 psi (4 hrs) (8hrs) (16 hrs) (2 hrs) (8 hrs) (16 hrs) Sample MB-5 45 g/g 48 g/g 52 g/g29 g/g 32 g/g 41 g/g Control Sample 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g20 g/g

A comparison of the PUP capacities indicates that the mixed-bedion-exchange absorbent polymer composition (Sample MB-5) absorbssubstantially more synthetic urine solution than the partiallyneutralized polyacrylate absorbent polymer (Control Sample) under thetest conditions described above.

(v) CUP Measurements

Approximately 0.9 grams of the mixed-bed ion-exchange absorbent polymercomposition (Sample MB-5) are transferred to a CUP cylinder (asdescribed in the Test Methods section above), and gently spread out overthe entire area of the screen comprising the base of the cylinder. CUPmeasurements are determined on separate samples under confiningpressures of 0.7 and 1.4 psi, with the amount of fluid absorbed measuredat frequent intervals for a period of 16 hours. The measured CUP at 0.7and 1.4 psi are shown as a function of time in FIGS. 5 and 6,respectively. Selected CUP data at 1, 2, 4, 8 and 16 hours arc listed inTable 10 below.

TABLE 10 CUP data for Mixed-bed Ion-exchange Absorbent PolymerCompositions 0.7 psi 0.7 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi 1.4 psi 1.4psi (1 hr) (4 hrs) (8 hrs) (16 hrs) (1 hr) (2 hrs) (8 hrs) (16 hrs)Sample MB-5 29 g/g 30 g/g 31 g/g 31 g/g 28 g/g 29 g/g 30 g/g 30 g/gControl Sample 21 g/g 21 g/g 22 g/g 22 g/g 13 g/g 13 g/g 15 g/g 17 g/g

A comparison of the CUP measurements indicates that the mixed-bedion-exchange absorbent polymer composition (Sample MB-5) absorbssubstantially more high ionic strength synthetic urine solution than thepartially neutralized polyacrylate absorbent polymer (Control Sample)under the test conditions described above.

The disclosures of all patents, patent applications (and any patentswhich issue thereon, as well as any corresponding published foreignpatent applications), and publications mentioned throughout thisdescription are hereby incorporated by reference herein, at least to theextent they are consistent with the terms and definitions of the presentdisclosure. It is expressly not admitted, however, that any of thedocuments incorporated by reference herein teach or disclose the presentinvention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A mixed-bed ion-exchange absorbent polymercomposition having a Performance Under Pressure (PUP) capacity insynthetic urine solution under an applied load of 0.7 psi of at leastabout 30 g/g after 2 hours.
 2. The mixed-bed ion-exchange composition ofclaim 1 having a PUP capacity in synthetic urine solution under anapplied load of 0.7 psi of at least about 32 g/g after 2 hours.
 3. Themixed-bed ion-exchange composition of claim 2 having a PUP capacity insynthetic urine solution under an applied load of 0.7 psi of at leastabout 35 g/g after 2 hours.
 4. The mixed-bed ion-exchange composition ofclaim 1 having a PUP capacity in synthetic urine solution under anapplied load of 0.7 psi of from about 30 g/g to about 49 g/g after 2hours.
 5. The mixed-bed ion-exchange composition of claim 4 having a PUPcapacity in synthetic urine solution under an applied load of 0.7 psi offrom about 32 g/g to about 47 g/g after 2 hours.
 6. The mixed-bedion-exchange composition of claim 5 having a PUP capacity in syntheticurine solution under an applied load of 0.7 psi of from about 35 g/g toabout 45 g/g after 2 hours.
 7. The mixed-bed ion-exchange composition ofclaim 1, wherein the ion-exchange capacity of the anion-exchangeabsorbent polymer is at least about 15 meq/g and the ion-exchangecapacity of the cation-exchange hydrogel-forming polymer is at leastabout 8 meq/g.
 8. A mixed-bed ion-exchange absorbent polymer compositionhaving a Performance Under Pressure (PUP) capacity in synthetic urinesolution under an applied load of 0.7 psi of at least about 40 g/g after8 hours.
 9. The mixed-bed ion-exchange composition of claim 8 having aPUP capacity in synthetic urine solution under an applied load of 0.7psi of at least about 42 g/g after 8 hours.
 10. The mixed-bedion-exchange composition of claim 9 having a PUP capacity in syntheticurine solution under an applied load of 0.7 psi of at least about 44 g/gafter 8 hours.
 11. The mixed-bed ion-exchange composition of claim 8having a PUP capacity in synthetic urine solution under an applied loadof 0.7 psi of from about 40 g/g to about 59 g/g after 8 hours.
 12. Themixed-bed ion-exchange composition of claim 11 having a PUP capacity insynthetic urine solution under an applied load of 0.7 psi of from about42 g/g to about 57 g/g after 8 hours.
 13. The mixed-bed ion-exchangecomposition of claim 12 having a PUP capacity in synthetic urinesolution under an applied lead of 0.7 psi of from about 44 g/g to about55 g/g after 8 hours.
 14. The mixed-bed ion-exchange composition ofclaim 8, wherein the ion-exchange capacity of the anion-exchangeabsorbent polymer is at least about 15 meq/g and the ion-exchangecapacity of the cation-exchange hydrogel-forming polymer is at leastabout 8 meq/g.
 15. A mixed-bed ion-exchange absorbent polymercomposition having a Performance Under Pressure (PUP) capacity insynthetic urine solution under an applied load of 0.7 psi of at leastabout 42 g/g after 16 hours.
 16. The mixed-bed ion-exchange compositionof claim 15 having a PUP capacity in synthetic urine solution under anapplied load of 0.7 psi of at least about 44 g/g after 16 hours.
 17. Themixed-bed ion-exchange composition of claim 16 having a PUP capacity insynthetic urine solution under an applied load of 0.7 psi of at leastabout 46 g/g after 16 hours.
 18. The mixed-bed ion-exchange compositionof claim 15 having a PUP capacity in synthetic urine solution under anapplied load of 0.7 psi of from about 42 g/g to about 61 g/g after 16hours.
 19. The mixed-bed ion-exchange composition of claim 18 having aPUP capacity in synthetic urine solution under an applied load of 0.7psi of from about 44 g/g to about 59 g/g after 16 hours.
 20. Themixed-bed ion-exchange composition of claim 19 having a PUP capacity insynthetic urine solution under an applied load of 0.7 psi of from about46 g/g to about 57 g/g after 16 hours.
 21. The mixed-bed ion-exchangecomposition of claim 20 having a PUP capacity in synthetic urinesolution under an applied load of 0.7 psi of from about 48 g/g to about54 g/g after 16 hours.
 22. The mixed-bed ion-exchange composition ofclaim 15, wherein the ion-exchange capacity of the anion-exchangeabsorbent polymer is at least about 15 meq/g and the ion-exchangecapacity of the cation-exchange hydrogel-forming polymer is at leastabout 8 meq/g.
 23. A mixed-bed ion-exchange absorbent polymercomposition having a Performance Under Pressure (PUP) capacity insynthetic urine solution under an applied load of 1.4 psi of at leastabout 27 g/g after 4 hours.
 24. The mixed-bed ion-exchange compositionof claim 23 having a PUP capacity in synthetic urine solution under anapplied load of 1.4 psi of at least about 32 g/g after 4 hours.
 25. Themixed-bed ion-exchange composition of claim 23 having a PUP capacity insynthetic urine solution under an applied load of 1.4 psi of from about27 g/g to about 46 g/g after 4 hours.
 26. The mixed-bed ion-exchangecomposition of claim 23 having a PUP capacity in synthetic urinesolution under an applied load of 1.4 psi of from about 32 g/g to about42 g/g after 4 hours.
 27. A mixed-bed ion-exchange absorbent polymercomposition having a Performance Under Pressure (PUP) capacity insynthetic urine solution under an applied load of 1.4 psi of at leastabout 30 g/g after 8 hours.
 28. The mixed-bed ion-exchange compositionof claim 27 having a PUP capacity in synthetic urine solution under anapplied load of 1.4 psi of at least about 35 g/g after 8 hours.
 29. Themixed-bed ion-exchange composition of claim 27 having a PUP capacity insynthetic urine solution under an applied load of 1.4 psi of from about30 g/g to about 49 g/g after 8 hours.
 30. The mixed-bed ion-exchangecomposition of claim 29 having a PUP capacity in synthetic urinesolution under an applied load of 1.4 psi of from about 35 g/g to about45 g/g after 8 hours.
 31. A mixed-bed ion-exchange absorbent polymercomposition having a Performance Under Pressure (PUP) capacity insynthetic urine solution under an applied load of 1.4 psi of at leastabout 33 g/g after 16 hours.
 32. The mixed-bed ion-exchange compositionof claim 31 having a PUP capacity in synthetic urine solution under anapplied load of 1.4 psi of at least about 38 g/g after 16 hours.
 33. Themixed-bed ion-exchange composition of claim 31 having a PUP capacity insynthetic urine solution under an applied load of 1.4 psi of from about33 g/g to about 52 g/g after 16 hours.
 34. The mixed-bed ion-exchangecomposition of claim 31 having a PUP capacity in synthetic urinesolution under an applied load of 1.4 psi of from about 38 g/g to about48 g/g after 16 hours.
 35. A mixed-bed ion-exchange absorbent polymercomposition comprising (i) a cation-exchange absorbent polymer; and (ii)an anion-exchange absorbent polymer, wherein the ion-exchange capacityof the anion-exchange absorbent polymer is at least about 15 meq/g. 36.The mixed-bed ion-exchange composition of claim 35, wherein thecation-exchange absorbent polymer is from about 80% to about 100% in theunneutralized acid form and the anion-exchange absorbent polymer is fromabout 80% to about 100% in the un-neutralized base form.
 37. Themixed-bed ion-exchange composition of claim 35, wherein the ion-exchangecapacity of the cation-exchange hydrogel-forming polymer is at leastabout 8 meq/g.
 38. The mixed-bed ion-exchange composition of claim 35,wherein the ion-exchange capacity of the anion-exchange absorbentpolymer is at least about 20 meq/g.
 39. The mixed-bed ion-exchangecomposition of claim 35, wherein the composition comprises ananion-exchange absorbent polymer having a multiplicity of unneutralizedprimary, secondary, and/or tertiary amine groups.
 40. The mixed-bedion-exchange composition of claim 35, wherein the composition comprisesan anion-exchange absorbent polymer prepared from a monomer selectedfrom the group consisting of ethylenimine, allylamine, diallylamine,4-aminobutene, alkyl oxazolines, vinylformamide, 5-aminopentene,carbodiimides, formaldazine, and melamine; a secondary amine derivativeof any of the foregoing; a tertiary amine derivative of any of theforegoing; and mixtures thereof.
 41. The mixed-bed ion-exchangecomposition of claim 35, wherein (i) the anion-exchange absorbentpolymer is prepared from a monomer selected from the group consisting ofethylenimine; allylamine; diallylamine; and mixtures thereof; and (ii)the cation-exchange polymer is prepared from acrylic acid monomers. 42.The mixed-bed ion-exchange composition of claim 41, wherein (i) theanion-exchange absorbent polymer is selected from the group consistingof poly(ethylenimine); poly(allylamine); and mixtures thereof; and (ii)the cation-exchange polymer is a homopolymer or copolymer of acrylicacid.
 43. The absorbent polymer composition of claim 35 having aPerformance Under Pressure (PUP) capacity in synthetic urine solutionunder an applied load of 0.7 psi of at least about 30 g/g after 2 hours.44. An absorbent polymer composition having a Performance Under Pressure(PUP) capacity in synthetic urine solution under an applied load of 0.7psi of at least about 42 g/g after 4 hours.
 45. The absorbent polymercomposition of claim 44 having a PUP capacity in synthetic urinesolution under an applied load of 0.7 psi of from about 42 g/g to about48 g/g after 4 hours.
 46. An absorbent polymer composition having aPerformance Under Pressure (PUP) capacity in synthetic urine solutionunder an applied load of 1.4 psi of at least about 32 g/g after 4 hours.47. The absorbent polymer composition of claim 46 having a PUP capacityin synthetic urine solution under an applied load of 1.4 psi of fromabout 35 g/g to about 40 g/g after 4 hours.
 48. An absorbent member forthe containment of aqueous body fluids, which comprises at least oneregion comprising the mixed-bed ion-exchange composition of claim
 1. 49.An absorbent member for the containment of aqueous body fluids, whichcomprises at least one region comprising the mixed-bed ion-exchangecomposition of claim
 8. 50. An absorbent member for the containment ofaqueous body fluids, which comprises at least one region comprising themixed-bed ion-exchange composition of claim
 15. 51. An absorbent memberfor the containment of aqueous body fluids, which comprises at least oneregion comprising the mixed-bed ion-exchange composition of claim 23.52. An absorbent member for the containment of aqueous body fluids,which comprises at least one region comprising the mixed-bedion-exchange composition of claim
 27. 53. An absorbent member for thecontainment of aqueous body fluids, which comprises at least one regioncomprising the mixed-bed ion-exchange composition of claim
 31. 54. Anabsorbent member for the containment of aqueous body fluids, whichcomprises at least one region comprising the mixed-bed ion-exchangecomposition of claim
 35. 55. An absorbent article comprising a liquidpervious topsheet, a backsheet and an absorbent core positioned betweenthe topsheet and the backsheet, wherein the absorbent core comprises theabsorbent member of claim
 48. 56. An absorbent article comprising aliquid pervious topsheet, a backsheet and an absorbent core positionedbetween the topsheet and the backsheet, wherein the absorbent corecomprises the absorbent member of claim
 49. 57. An absorbent articlecomprising a liquid pervious topsheet, a backsheet and an absorbent corepositioned between the topsheet and the backsheet, wherein the absorbentcore comprises the absorbent member of claim
 50. 58. An absorbentarticle comprising a liquid pervious topsheet, a backsheet and anabsorbent core positioned between the topsheet and the backsheet,wherein the absorbent core comprises the absorbent member of claim 51.59. An absorbent article comprising a liquid pervious topsheet, abacksheet and an absorbent core positioned between the topsheet and thebacksheet, wherein the absorbent core comprises the absorbent member ofclaim
 52. 60. An absorbent article comprising a liquid pervioustopsheet, a backsheet and an absorbent core positioned between thetopsheet and the backsheet, wherein the absorbent core comprises theabsorbent member of claim
 53. 61. An absorbent article comprising aliquid pervious topsheet, a backsheet and an absorbent core positionedbetween the topsheet and the backsheet, wherein the absorbent corecomprises the absorbent member of claim
 54. 62. A mixed-bed ion-exchangeabsorbent polymer composition having a Capacity Under Pressure (CUP) inhigh ionic strength synthetic urine solution under an applied load of0.7 psi of at least about 23 g/g after 1 hour.
 63. The mixed-bedion-exchange composition of claim 62 having a Capacity Under Pressure(CUP) in high ionic strength synthetic urine solution under an appliedload of 0.7 psi of from about 23 g/g to about 35 g/g after 1 hour.
 64. Amixed-bed ion-exchange absorbent polymer composition having a CapacityUnder Pressure (CUP) in high ionic strength synthetic urine solutionunder an applied load of 0.7 psi of at least about 25 g/g after 4 hours.65. The mixed-bed ion-exchange composition of claim 64 having a CapacityUnder Pressure (CUP) in high ionic strength synthetic urine solutionunder an applied load of 0.7 psi of at least about 27 g/g after 4 hours.66. The mixed-bed ion-exchange composition of claim 62 having a CapacityUnder Pressure (CUP) in high ionic strength synthetic urine solutionunder an applied load of 0.7 psi of at least about 30 g/g after 4 hours.67. The mixed-bed ion-exchange composition of claim 62 having a CapacityUnder Pressure (CUP) in high ionic strength synthetic urine solutionunder an applied load of 0.7 psi of from about 25 g/g to about 35 g/gafter 4 hours.
 68. The mixed-bed ion-exchange composition of claim 67having a Capacity Under Pressure (CUP) in high ionic strength syntheticurine solution under an applied load Of 0.7 psi of from about 27 g/g toabout 33 g/g after 4 hours.
 69. A mixed-bed ion-exchange absorbentpolymer composition having a Capacity Under Pressure (CUP) in high ionicstrength synthetic urine solution under an applied load of 0.7 psi of atleast about 27 g/g after 8 hours.
 70. The mixed-bed ion-exchangecomposition of claim 69 having a Capacity Under Pressure (CUP) in highionic strength synthetic urine solution under an applied load of 0.7 psiof at least about 29 g/g after 8 hours.
 71. The mixed-bed ion-exchangecomposition of claim 70 having a Capacity Under Pressure (CUP) in highionic strength synthetic urine solution under an applied load of 0.7 psiof at least about 31 g/g after 8 hours.
 72. The mixed-bed ion-exchangecomposition of claim 69 having a Capacity Under Pressure (CUP) in highionic strength synthetic urine solution under an applied load of 0.7 psiof from about 27 g/g to about 37 g/g after 8 hours.
 73. The mixed-bedion-exchange composition of claim 72 having a Capacity Under Pressure(CUP) in high ionic strength synthetic urine solution under an appliedload of 0.7 psi of from about 29 g/g to about 33 g/g after 4 hours. 74.A mixed-bed ion-exchange absorbent polymer composition having a CapacityUnder Pressure (CUP) in high ionic strength synthetic urine solutionunder an applied load of 1.4 psi of at least about 20 g/g after 2 hours.75. The mixed-bed ion-exchange composition of claim 74 having a CapacityUnder Pressure (CUP) in high ionic strength synthetic urine solutionunder an applied load of 1.4 psi of at least about 23 g/g after 2 hours.76. The mixed-bed ion-exchange composition of claim 75 having a CapacityUnder Pressure (CUP) in high ionic strength synthetic urine solutionunder an applied load of 1.4 psi of at least about 27 g/g after 2 hours.77. The mixed-bed ion-exchange composition of claim 74 having a CapacityUnder Pressure (CUP) in high ionic strength synthetic urine solutionunder an applied load of 1.4 psi of from about 20 g/g to about 35 g/gafter 2 hours.
 78. The mixed-bed ion-exchange composition of claim 77having a Capacity Under Pressure (CUP) in high ionic strength syntheticurine solution under an applied load of 1.4 psi of from about 23 g/g toabout 32 g/g after 2 hours.
 79. A mixed-bed ion-exchange absorbentpolymer composition having a Capacity Under Pressure (CUP) in high ionicstrength synthetic urine solution under an applied load of 1.4 psi of atleast about 22 g/g after 8 hours.
 80. The mixed-bed ion-exchangecomposition of claim 79 having a Capacity Under Pressure (CUP) in highionic strength synthetic urine solution under an applied load of 1.4 psiof at least about 25 g/g after 8 hours.
 81. The mixed-bed ion-exchangecomposition of claim 80 having a Capacity Under Pressure (CUP) in highionic strength synthetic urine solution under an applied load of 1.4 psiof at least about 27 g/g after 8 hours.
 82. The mixed-bed ion-exchangecomposition of claim 74 having a Capacity Under Pressure (CUP) in highionic strength synthetic urine solution under an applied load of 1.4 psiof from about 22 g/g to about 35 g/g after 8 hours.
 83. The mixed-bedion-exchange composition of claim 82 having a Capacity Under Pressure(CUP) in high ionic strength synthetic urine solution under an appliedload of 1.4 psi of from about 25 g/g to about 33 g/g after 8 hours. 84.An absorbent member for the containment of aqueous body fluids, whichcomprises at least one region comprising the mixed-bed ion-exchangecomposition of claim
 62. 85. An absorbent member for the containment ofaqueous body fluids, which comprises at least one region comprising themixed-bed ion-exchange composition of claim
 67. 86. An absorbent memberfor the containment of aqueous body fluids, which comprises at least oneregion comprising the mixed-bed ion-exchange composition of claim 72.87. An absorbent member for the containment of aqueous body fluids,which comprises at least one region comprising the mixed-bedion-exchange composition of claim
 77. 88. An absorbent articlecomprising a liquid pervious topsheet, a backsheet and an absorbent corepositioned between the topsheet and the backsheet, wherein the absorbentcore comprises the absorbent member of claim
 84. 89. An absorbentarticle comprising a liquid pervious topsheet, a backsheet and anabsorbent core positioned between the topsheet and the backsheet,wherein the absorbent core comprises the absorbent member of claim 85.90. An absorbent article comprising a liquid pervious topsheet, abacksheet and an absorbent core positioned between the topsheet and thebacksheet, wherein the absorbent core comprises the absorbent member ofclaim
 86. 91. An absorbent article comprising a liquid pervioustopsheet, a backsheet and an absorbent core positioned between thetopsheet and the backsheet, wherein the absorbent core comprises theabsorbent member of claim
 87. 92. The mixed-bed ion-exchange compositionof claim 62, wherein the composition comprises: (i) an anion-exchangeabsorbent polymer prepared from a monomer selected from the groupconsisting of ethylenitnine; allylamine; vinylformamide; and mixturesthereof; and (ii) a cation-exchange polymer is prepared from acrylicacid monomers, wherein the cation exchange polymer is homogeneouslycrosslinked.
 93. A mixed-bed ion-exchange composition wherein thecomposition comprises: (i) an anion exchange absorbent polymer preparedfrom a monomer selected from the group consisting of ethylenimine;allylamine; vinylformamide; and mixtures thereof; and (ii) a cationexchange absorbent polymer prepared from acrylic acid monomers; whereinthe anion exchange absorbent polymer and the cation-exchange absorbentpolymer are blended so as to provide a particle morphology suitable forfast ion exchange kinetics, the morphology being selected from the groupconsisting of: a) aggregates of high-surface-area particles; b)particles wherein the anion-exchange absorbent polymer contain smaller,discontinuous domains of the cation-exchange absorbent polymer dispersedtherein; c) particles wherein the cation-exchange absorbent polymercontains smaller, discontinuous domains of the anion-exchange absorbentpolymer dispersed therein; and d) particles that contain bicontinuousdomains of the both anion- and cation-exchange absorbent polymers.
 94. Amixed-bed ion-exchange composition according to claim 93 wherein thedomains prepared using a blending technique selected from the groupconsisting of high ear blending, ball milling, and pin milling.